handshake-capture-c6 v1.0.4: persist captured BSSIDs, PCAP EAPOL recount

- /cap_bssids.txt append on save; handshakeLoadPersistedBssids after SD mount
- Boot order: SD then load file then first WiFi scan (reds match SD)
- Pre-save walk of in-memory PCAP counting EAPOL-Key frames
- SD_AppendLine / SD_ForEachLine; drop g_sd_ready clear on write fail
- README + MUST_DO updates

Made-with: Cursor

handshake-capture-c6/SD_Card.h

@@ -16,3 +16,8 @@ bool SD_Init();
  */
 bool SD_IsReady();
 bool SD_WriteFileAtomic(const char* path, const uint8_t* data, size_t len);
+/** Append one line (caller supplies \\n if desired). Uses same SPI lock as other SD ops. */
+bool SD_AppendLine(const char* path, const char* line);
+typedef void (*SD_LineCallback)(const char* line, void* user);
+/** Read text file line-by-line; missing file is OK (returns true). */
+bool SD_ForEachLine(const char* path, SD_LineCallback cb, void* user);