feat: incident correlation overhaul, signal-based auto-resolve, token fixes

Correlator
- Raise fast-path idle gate 30 → 90 min (tg_fast_path_idle_minutes)
- Fix disambiguate always-commits bug: run _call_fits_incident on winner
  before committing; fall through to new-incident creation if it fails
- Add unit-continuity path (path 1.5): matches all_active by shared unit
  IDs with a reassignment guard, bridges calls past the idle gate
- Add tag-based incident_type inference (_TAG_TYPE_HINTS) as GPT fallback,
  rescuing tagged calls that would have been dropped (616 observed orphans)
- Add master/child incident model: _create_master_incident, _demote_to_child,
  _add_child_to_master; new incidents stamped incident_type="master"
- Add cross-system parent detection (_find_cross_system_parent): two-signal
  scoring (road overlap=0.4, embedding≥0.78=0.3, proximity=0.3, threshold=0.5)
  wired into create-if-new path; creates master shell on first cross-system match
- Add maybe_resolve_parent: auto-resolves master when all children close;
  called from upload pipeline (LLM closure) and summarizer stale sweep
- Add signal-based auto-resolve via units_active/units_cleared tracking:
  GPT now extracts cleared_units per scene; _update_incident moves units
  between active/cleared lists and resolves the incident when active empties;
  stored on call doc for re-correlation sweep reuse
- Add _create_incident initialization of units_active/units_cleared fields

Re-correlation sweep
- Add corr_sweep_count + MAX_SWEEP_ATTEMPTS=3: orphans get 3 attempts
  then are tombstoned as corr_path="unlinked", ending the re-sweep loop
  (previously hammering each orphan 29-31 times per shift)

Intelligence extraction
- Add cleared_units to GPT prompt schema and rules
- Extract and propagate cleared_units per scene; merge across scenes;
  store on call doc for re-correlation sweep

Token management
- Fix token release bug: remove release_token call on discord_connected=False
  in MQTT checkin (transient Discord drops were orphaning bots mid-shift)
- Add PUT /tokens/{id}/prefer/{system_id} endpoint: lock a bot token to a
  system; pass _none as system_id to clear; stored bidirectionally on both
  token and system documents
- discord_join handler resolves preferred_token_id from system doc and passes
  system_name in MQTT payload

drb-c2-core/app/internal/mqtt_handler.py

@@ -109,10 +109,11 @@ class MQTTHandler:
                 updates["status"] = "online"
             await fstore.doc_update("nodes", node_id, updates)
 
-        # Release any orphaned Discord token when the node explicitly reports disconnected
-        if payload.get("discord_connected") is False:
-            from app.routers.tokens import release_token
-            await release_token(node_id)
+        # NOTE: discord_connected in checkins is informational only — do NOT release the
+        # token here.  The bot watchdog reconnects on transient Discord drops, so a single
+        # checkin with discord_connected=False during a brief reconnect window would
+        # incorrectly free the token while the bot is still active.  Token release is
+        # handled exclusively by the discord_leave command and the node offline sweeper.
 
     # ------------------------------------------------------------------
     # Status update