Expand test coverage across server, agent, and web; fix bugs found during audit.

Adds hundreds of unit/integration/e2e tests, fixes WS bcrypt auth, config merge, fleet analytics, agent schedule/log tail, and documents stale PROBLEMS items. Updates PROBLEMS.md, README, and test scripts; ignores local spread-kits and coverage dirs.

server/internal/db/agent_meta.go

@@ -2,6 +2,7 @@ package db
 
 import (
 	"encoding/json"
+	"log"
 	"strings"
 
 	"crypto-miner-server/internal/models"
@@ -14,6 +15,7 @@ func decodeTags(raw string) []string {
 	}
 	var tags []string
 	if err := json.Unmarshal([]byte(raw), &tags); err != nil {
+		log.Printf("[db] decodeTags: corrupt tags JSON ignored (%v): %q", err, raw)
 		return []string{}
 	}
 	return tags