fix(security): A-3 auth middleware coverage fixes

Fixes 9 auth middleware findings from the A-3 recon audit.

F-A3-11 CRITICAL: Removed JWT secret from WebAuthMiddleware log output.
  Replaced emoji-prefixed fmt.Printf with ETHOS-compliant log.Printf.
  No secret values in any log output.

F-A3-7 CRITICAL: Config download now requires WebAuthMiddleware.
  GET /downloads/config/:agent_id is admin-only (agents never call it).

F-A3-6 HIGH: Update package download now requires AuthMiddleware.
  GET /downloads/updates/:package_id requires valid agent JWT.

F-A3-10 HIGH: Scheduler stats changed from AuthMiddleware to
  WebAuthMiddleware. Agent JWTs can no longer view scheduler internals.

F-A3-13 LOW: RequireAdmin() middleware implemented. 7 security settings
  routes re-enabled (GET/PUT/POST under /security/settings).
  security_settings.go.broken renamed to .go, API mismatches fixed.

F-A3-12 MEDIUM: JWT issuer claims added for token type separation.
  Agent tokens: issuer=redflag-agent, Web tokens: issuer=redflag-web.
  AuthMiddleware rejects tokens with wrong issuer.
  Grace period: tokens with no issuer still accepted (backward compat).

F-A3-2 MEDIUM: /auth/verify now has WebAuthMiddleware applied.
  Endpoint returns 200 with valid=true for valid admin tokens.

F-A3-9 MEDIUM: Agent self-unregister (DELETE /:id) now rate-limited
  using the same agent_reports rate limiter as other agent routes.

F-A3-14 LOW: CORS origin configurable via REDFLAG_CORS_ORIGIN env var.
  Defaults to http://localhost:3000 for development.
  Added PATCH method and agent-specific headers to CORS config.

All 27 server tests pass. All 14 agent tests pass. No regressions.
See docs/A3_Fix_Implementation.md and docs/Deviations_Report.md
(DEV-020 through DEV-022).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

aggregator-server/.env.example

@@ -10,3 +10,6 @@ JWT_SECRET=change-me-in-production-use-long-random-string
 # Agent Configuration
 CHECK_IN_INTERVAL=300          # seconds
 OFFLINE_THRESHOLD=600          # seconds before marking agent offline
+
+# CORS Configuration (default: http://localhost:3000)
+# REDFLAG_CORS_ORIGIN=https://your-dashboard-domain.com