docs: update AGENTS.md hierarchy with new subdirectory docs

- Update root AGENTS.md with expanded anti-patterns and notes
- Add handler/AGENTS.md for high-complexity backend handlers
- Add connector/AGENTS.md for GOST connector protocols
- Add socket/AGENTS.md for GOST socket utilities

go-backend/internal/http/handler/AGENTS.md

@@ -0,0 +1,43 @@
+# BACKEND HTTP HANDLER KNOWLEDGE BASE
+
+**Generated:** Fri Feb 13 2026
+
+## OVERVIEW
+HTTP request handlers for FLVX Admin API. Core business logic layer.
+**Stack:** Go 1.23, net/http, raw SQL (no ORM).
+
+## STRUCTURE
+```
+handler/
+├── handler.go        # Main Handler struct, login/captcha, job scheduling
+├── control_plane.go  # Node control plane API (add/delete/list)
+├── federation.go     # Federation/cluster sync API
+├── flow_policy.go    # Traffic policy API
+├── jobs.go           # Background job management (sync, cleanup)
+├── mutations.go      # CRUD for users, tunnels, forwards (largest: 100k+ LOC)
+└── upgrade.go        # System upgrade API
+```
+
+## WHERE TO LOOK
+| Task | Location | Notes |
+|------|----------|-------|
+| **User/Tunnel CRUD** | `mutations.go` | Largest file; all create/update/delete ops |
+| **Login/Captcha** | `handler.go` | Login flow, captcha verification |
+| **Federation Sync** | `federation.go` | Panel-to-panel sync |
+| **Traffic Policies** | `flow_policy.go` | Flow limiting, quota management |
+| **Background Jobs** | `jobs.go` | Scheduled sync/cleanup tasks |
+
+## CONVENTIONS
+- Inherits from parent: raw SQL, no ORM, JWT in Authorization header.
+- Large files expected (`mutations.go` >100k LOC).
+- Uses `sqlite.Repository` for DB access via `repo.XXX()` methods.
+
+## ANTI-PATTERNS
+- Do NOT add ORM here - uses raw SQL throughout.
+- Do NOT change handler signatures without updating router.go.
+
+## COMMANDS
+```bash
+cd go-backend
+go test ./internal/http/handler/...
+```