feat(bug-fast-track): cheaper/shorter pipeline route for bug-fix tasks (ORCH-019)

A task carrying the Plane `Bug` label takes a shortened route that skips the
`architecture` stage (one opus architect run + ADR + check_architecture_done),
replacing heavy analysis with a lite package (bug-report + mandatory regression
test plan). EVERY Quality Gate / sub-gate runs UNCHANGED — the route is a
scheduler property, not a gate (root invariant NFR-1): STAGE_TRANSITIONS /
QG_CHECKS / check_* / machine-verdict keys are byte-for-byte preserved.

- src/bug_fast_track.py: new leaf (never-raise) — bug_fast_track_applies (local,
  network-free, checked first), is_bug_task (labels.has_label, Plane API source),
  skips_architecture (pure DB-backed routing predicate), snapshot.
- src/db.py: additive idempotent tasks.track column (TEXT DEFAULT 'full') +
  set_task_track / get_task_track helpers (missing/NULL -> 'full', fail-safe).
- src/stage_engine.py: routing-override on the analysis-exit edge (track='bug' ->
  development/developer, skipping architect); brd-review-clock stamp extended to
  analysis->development. get_next_stage/get_agent_for_stage stay pure.
- src/webhooks/plane.py: classify task as bug in start_pipeline (applies-first
  short-circuit; never-raise -> full cycle on any error).
- src/main.py: additive bug_fast_track block in GET /queue + POST
  /bug-fast-track/escalate (reset 'bug'->'full' to return to the full cycle).
- src/config.py: bug_fast_track_enabled / _label / _repos flags (empty CSV ->
  self-hosting only).
- src/notifications.py: optional 🐞 marker on the bug-track card (never-raise).
- Prompts: analyst.md (lite bug package + escalation), reviewer.md (regression-
  test axis) — 52d canon preserved.
- Docs: CLAUDE.md, README.md (env + API + section), docs/architecture/README.md,
  CHANGELOG.md, .env.example.
- Tests: tests/test_bug_fast_track*.py + test_db_migrations.py + queue block
  (TC-01..TC-15). Full regression green (1551 passed).

Kill-switch ORCH_BUG_FAST_TRACK_ENABLED=false -> 1:1 pre-ORCH-019 (zero
regression; residual track column harmless).

Refs: ORCH-019

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_queue_endpoint.py

@@ -59,3 +59,50 @@ def test_queue_serial_gate_reflects_freeze():
     assert "orchestrator" in per
     assert per["orchestrator"]["frozen"] is True
     assert per["orchestrator"]["frozen_reason"] == "DEGRADED"
+
+
+# --- ORCH-019 (TC-13): additive bug_fast_track block -----------------------
+def test_queue_has_bug_fast_track_block_and_keeps_existing_keys(monkeypatch):
+    import asyncio
+    from src import main
+
+    monkeypatch.setattr(cfg.settings, "bug_fast_track_enabled", True, raising=False)
+    payload = asyncio.run(main.queue())
+
+    # Pre-existing keys are all still present (no contract break).
+    for key in ("counts", "serial_gate", "coverage", "auto_labels", "stop", "recent"):
+        assert key in payload, f"existing /queue key '{key}' must be preserved"
+
+    assert "bug_fast_track" in payload
+    bft = payload["bug_fast_track"]
+    assert bft["enabled"] is True
+    assert set(bft) >= {
+        "enabled", "label", "repos",
+        "active_bug_tasks", "total_bug_tasks", "est_saved_architecture_runs",
+    }
+
+
+def test_queue_bug_fast_track_counts_bug_tasks():
+    import asyncio
+    from src import main
+
+    conn = db.get_db()
+    conn.execute(
+        "INSERT INTO tasks (plane_id, work_item_id, repo, branch, stage, title, track) "
+        "VALUES ('p1','ORCH-401','orchestrator','feature/x','development','t','bug')"
+    )
+    conn.execute(
+        "INSERT INTO tasks (plane_id, work_item_id, repo, branch, stage, title, track) "
+        "VALUES ('p2','ORCH-402','orchestrator','feature/y','done','t','bug')"
+    )
+    conn.execute(
+        "INSERT INTO tasks (plane_id, work_item_id, repo, branch, stage, title, track) "
+        "VALUES ('p3','ORCH-403','orchestrator','feature/z','development','t','full')"
+    )
+    conn.commit()
+    conn.close()
+
+    bft = asyncio.run(main.queue())["bug_fast_track"]
+    assert bft["total_bug_tasks"] == 2          # two bug tasks total
+    assert bft["active_bug_tasks"] == 1         # one non-terminal bug task
+    assert bft["est_saved_architecture_runs"] == 2