feat(frontend): unlocks/inventory UI, sigil designer, listening-tool EVP threshold

Workstream F of the character-depth/ghost-log spec.

- InventoryPanel.tsx: essence balance, owned unlocks/items (terminal
  listing + Codex-style rarity-glow borders on items), and a buy flow
  for a small fixed unlock catalog (currently just "listening_tool",
  the only key the contract names) with afford/can't-afford button
  states. Prices are fetched from a best-guess /api/inventory/catalog
  endpoint and fall back to a flagged "(est.)" price sourced from the
  spec's own worked example when that endpoint isn't available yet —
  the contract doesn't define a price-list REST shape.

- SigilDesigner.tsx + lib/sigil.ts: constrained geometric builder —
  points snap to 24 fixed clock-face slots around a circle, capped at
  12 to match the backend's payload limit, connected in placement
  order. Five hand-drawn stroke-only rune glyphs (eye/crescent/key/
  spiral/thorn) overlay the center. Point-cap enforcement, rune
  selection and payload-shape building are pure functions in
  lib/sigil.ts, unit-tested directly. Saves via POST
  /api/inventory/sigils (path inferred; payload shape matches the
  contract exactly: {"points": [[x,y],...], "rune": str}). Art
  direction: the builder itself reads like a plotting/debug tool
  (crosshair cursor, monospace coordinate HUD) while the rendered
  lines + rune glow violet, consistent with GhostGlyph's conventions.

- lib/evp.ts: new evpThresholdDb(hasListeningTool) pure function and
  EvpListener.start() now accepts { hasListeningTool } to lower the
  EVP anomaly threshold (8dB -> 4dB) when the unlock is owned — wired
  from useAuth().user.unlocks in SeancePage's EvpPanel, a real
  gameplay effect on which faint signals register as anomalies.

- api.ts User type gains unlocks/essence per the contract's /auth/me
  extension; new InventoryPage.tsx mounts both components behind auth
  at /inventory, linked from the séance nav.

166/166 tests pass (137 pre-existing + 29 new), i18n coverage check
clean, tsc -b clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/InventoryPanel.test.tsx

@@ -0,0 +1,136 @@
+import { render, screen, waitFor } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import '../i18n'
+import { InventoryPanel } from './InventoryPanel'
+
+function mockFetch(handlers: {
+  items?: unknown
+  itemsStatus?: number
+  catalog?: unknown
+  catalogStatus?: number
+  purchaseStatus?: number
+}) {
+  vi.stubGlobal(
+    'fetch',
+    vi.fn(async (input: RequestInfo | URL, init?: RequestInit) => {
+      const url = String(input)
+      if (url.includes('/api/inventory/items')) {
+        return new Response(JSON.stringify(handlers.items ?? { items: [] }), {
+          status: handlers.itemsStatus ?? 200,
+          headers: { 'Content-Type': 'application/json' },
+        })
+      }
+      if (url.includes('/api/inventory/catalog')) {
+        if (handlers.catalogStatus && handlers.catalogStatus !== 200) {
+          return new Response('not found', { status: handlers.catalogStatus })
+        }
+        return new Response(JSON.stringify(handlers.catalog ?? { unlocks: [] }), {
+          status: 200,
+          headers: { 'Content-Type': 'application/json' },
+        })
+      }
+      if (url.includes('/api/inventory/unlocks/') && init?.method === 'POST') {
+        return new Response('{}', { status: handlers.purchaseStatus ?? 200 })
+      }
+      return new Response('not found', { status: 404 })
+    }),
+  )
+}
+
+describe('InventoryPanel', () => {
+  beforeEach(() => {
+    vi.restoreAllMocks()
+  })
+
+  afterEach(() => {
+    vi.unstubAllGlobals()
+  })
+
+  it('shows the essence balance prominently', async () => {
+    mockFetch({ catalog: { unlocks: [{ unlock_key: 'listening_tool', price: 40 }] } })
+    render(<InventoryPanel unlocks={[]} essence={128} />)
+    expect(screen.getByTestId('essence-value').textContent).toBe('128')
+    await screen.findByRole('button', { name: /buy/i }) // let pending fetches settle
+  })
+
+  it('lists owned unlocks with an [OWNED] tag and hides them from the buy catalog', async () => {
+    mockFetch({ catalog: { unlocks: [{ unlock_key: 'listening_tool', price: 40 }] } })
+    render(<InventoryPanel unlocks={['listening_tool']} essence={5} />)
+    expect(await screen.findByText('listening_tool')).toBeTruthy()
+    expect(screen.getByText('[OWNED]')).toBeTruthy()
+    expect(screen.queryByRole('button', { name: /buy/i })).toBeNull()
+  })
+
+  it('disables the buy button when the user cannot afford the unlock', async () => {
+    mockFetch({ catalog: { unlocks: [{ unlock_key: 'listening_tool', price: 40 }] } })
+    render(<InventoryPanel unlocks={[]} essence={10} />)
+    const btn = await screen.findByRole('button', { name: /buy/i })
+    await waitFor(() => expect(btn).toHaveProperty('disabled', true))
+  })
+
+  it('enables the buy button when the user can afford the unlock', async () => {
+    mockFetch({ catalog: { unlocks: [{ unlock_key: 'listening_tool', price: 40 }] } })
+    render(<InventoryPanel unlocks={[]} essence={100} />)
+    const btn = await screen.findByRole('button', { name: /buy/i })
+    await waitFor(() => expect(btn).toHaveProperty('disabled', false))
+  })
+
+  it('falls back to a flagged estimated price when the catalog endpoint is unavailable', async () => {
+    mockFetch({ catalogStatus: 404 })
+    render(<InventoryPanel unlocks={[]} essence={100} />)
+    await waitFor(() => expect(screen.getByText(/\(est\.\)/)).toBeTruthy())
+    const btn = screen.getByRole('button', { name: /buy/i })
+    expect(btn).toHaveProperty('disabled', false) // 100 essence affords the 40 fallback price
+  })
+
+  it('purchasing successfully moves the unlock into the owned list and deducts essence', async () => {
+    mockFetch({
+      catalog: { unlocks: [{ unlock_key: 'listening_tool', price: 40 }] },
+      purchaseStatus: 200,
+    })
+    const user = userEvent.setup()
+    render(<InventoryPanel unlocks={[]} essence={100} />)
+    const btn = await screen.findByRole('button', { name: /buy/i })
+    await waitFor(() => expect(btn).toHaveProperty('disabled', false))
+    await user.click(btn)
+
+    await waitFor(() => expect(screen.getByTestId('essence-value').textContent).toBe('60'))
+    expect(screen.getByText('[OWNED]')).toBeTruthy()
+    expect(screen.queryByRole('button', { name: /buy/i })).toBeNull()
+  })
+
+  it('shows an insufficient-funds message on a 402 without changing essence', async () => {
+    mockFetch({
+      catalog: { unlocks: [{ unlock_key: 'listening_tool', price: 40 }] },
+      purchaseStatus: 402,
+    })
+    const user = userEvent.setup()
+    render(<InventoryPanel unlocks={[]} essence={100} />)
+    const btn = await screen.findByRole('button', { name: /buy/i })
+    await waitFor(() => expect(btn).toHaveProperty('disabled', false))
+    await user.click(btn)
+
+    await screen.findByRole('alert')
+    expect(screen.getByTestId('essence-value').textContent).toBe('100')
+  })
+
+  it('renders items with a rarity data attribute when payload carries a known rarity', async () => {
+    mockFetch({
+      items: {
+        items: [
+          {
+            item_type: 'trinket',
+            item_key: 'silver-locket',
+            payload: { rarity: 'rare' },
+            obtained_at: '2026-01-01T00:00:00Z',
+          },
+        ],
+      },
+    })
+    render(<InventoryPanel unlocks={[]} essence={0} />)
+    const key = await screen.findByText('silver-locket')
+    const card = key.closest('[data-rarity]')
+    expect(card?.getAttribute('data-rarity')).toBe('rare')
+  })
+})