feat(intentions): Phase 7 — if-then rules for task / time / triage triggers

Small if-then automation layer. Rules persist in SQLite; the runner
lives on the frontend and binds to the Phase 6 event bus so the rule
pipeline reuses the same delivery primitives (timer events, TTS,
Tasks navigation).

Storage:
- Migration v12 adds implementation_rules (id, enabled, trigger_kind,
  trigger_value, actions_json, last_fired_key, created_at,
  updated_at) with enabled+trigger_kind index for the runner's hot
  path.
- CRUD helpers: insert / list / get / set-enabled / mark-fired /
  delete, plus a round-trip test.

Commands (all main-window-guarded via ensure_main_window):
- list_implementation_rules
- create_implementation_rule — validates HH:MM, checks the target
  task exists at save time for surface-task actions, caps
  speak-line at 240 chars, pins v1 timers to 5 minutes.
- set_implementation_rule_enabled
- mark_implementation_rule_fired — main-thread idempotency shim so
  the runner can atomically claim a fire.
- delete_implementation_rule

Runner (implementationIntentions.svelte.ts):
- Subscribes to kon:task-completed and kon:morning-triage-finished
  (MorningTriageModal now emits on all three exit paths — empty,
  skipped, picked — so skip counts as finishing).
- 30 s poll for time-of-day rules, plus an immediate check on startup
  so a rule whose time has already passed today catches up once.
- Idempotency via last_fired_key composed as YYYY-MM-DD@HH:MM for
  time rules; new time rules whose HH:MM has already passed today
  are pre-seeded so they don't fire retroactively on save.
- Rules are paused when Nudges "Mute for now" is on — a hard mute
  stops all rule delivery in addition to OS notifications.
- Stale-task safety: if a surface-task action's target has been
  deleted, the runner opens Tasks and warns clearly rather than
  pretending to surface something that's gone.

Editor (ImplementationRulesEditor.svelte):
- Lives in Settings under a new "If-then rules" accordion section.
- `If` picker: time of day (with time input), a task completes,
  morning triage finishes.
- `Then` composer: optional surface (inbox / today / all tasks /
  specific task), optional 5-min timer, optional speak-aloud line.
- Saved rules list with enable toggle + delete.

Rules table integration for Phase 10b rename sweep: add
implementation_rules to the kon.db → corbie.db migration shim when
that phase lands.

Gates: fmt, clippy -D warnings, cargo test 265/0, svelte-check
0/0, npm build green. Pre-existing Vite chunk warning on sounds.ts
is unrelated to Phase 7.

src/lib/components/MorningTriageModal.svelte

@@ -60,6 +60,13 @@
     return d.getHours() * 60 + d.getMinutes();
   }
 
+  function dispatchTriageFinished(mode: 'empty' | 'skipped' | 'picked') {
+    if (typeof window === 'undefined') return;
+    window.dispatchEvent(new CustomEvent('kon:morning-triage-finished', {
+      detail: { date: todayKey(), mode },
+    }));
+  }
+
   function isBeforeToday(createdAt: string): boolean {
     // Task `createdAt` comes from SQLite as ISO-8601 UTC. Compare the
     // local-time date portion so a task made last night locally counts
@@ -100,6 +107,7 @@
       // Nothing to triage — record the shown sentinel anyway so we
       // don't re-check the DB every focus event today.
       try { await invoke('mark_morning_triage_shown', { date: todayKey() }); } catch {}
+      dispatchTriageFinished('empty');
       return;
     }
 
@@ -133,6 +141,7 @@
     } finally {
       applying = false;
       open = false;
+      dispatchTriageFinished('skipped');
     }
   }
 
@@ -158,6 +167,7 @@
     } finally {
       applying = false;
       open = false;
+      dispatchTriageFinished('picked');
     }
   }