Implement A9 state-change logging in the state store

Retrofit for the conventions merged in #4 (issue #3):

- OpLog: JSON-lines emitter with the fixed envelope (ts, agent,
  event, task_id, cause); task_id set by the orchestrator at
  unit-of-work start
- StateStore owns emission: transition, intent begin/commit/abort,
  and schema migrations each emit their event right after the
  durable write commits; callers pass the cause
- reconcile_on_boot emits boot.reconcile with action and verdicts,
  and resolves intents with reconciliation-verdict causes
- Failed resolutions emit nothing (a line exists iff the write
  committed)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nisse-dev/src/nisse_dev/reconcile.py

@@ -39,15 +39,23 @@ def reconcile_on_boot(
             continue
         verdict = reconciler(intent)
         if verdict is True:
-            store.commit_intent(intent.id)
+            store.commit_intent(
+                intent.id, cause="reconciliation verdict: effect verified"
+            )
             notes.append(f"{label}: external effect verified, marked committed")
         elif verdict is False:
-            store.abort_intent(intent.id)
+            store.abort_intent(
+                intent.id, cause="reconciliation verdict: never took effect"
+            )
             notes.append(f"{label}: never took effect, marked aborted")
         else:
             unresolved = True
             notes.append(f"{label}: unverifiable")
-    return BootReport(
+    report = BootReport(
         action="await_input" if unresolved else "resume",
         notes=notes,
     )
+    store.oplog.emit(
+        "boot.reconcile", cause="startup", action=report.action, verdicts=notes
+    )
+    return report