feat(schema): protobuf event registry + buf CI gate (#54)

- Add proto schemas in packages/shared-types/events/ (oo.events.v1):
  envelope.proto, signals.proto, integration.proto
- buf.yaml with STANDARD lint + FILE breaking-change rules
- .gitea/workflows/buf-check.yaml: lint + breaking check on every PR
  touching events/ (needs a Gitea Actions runner to execute)
- scripts/buf-check.sh: local equivalent of the CI check
- NormalizedEvent TS envelope gains eventId, schemaVersion, producer
  to align with the proto Envelope message
- ml/serving/schemas.py: pydantic models mirroring the v1 proto types
- nats_consumer.py: validate payloads via pydantic instead of raw .get()

A field-rename PR will now fail buf breaking with exit code 100 and
show the offending messages. To make a breaking change: keep the old
field reserved, add the new one, bump schema_version to v2.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/shared-types/src/events/index.ts

@@ -1,6 +1,6 @@
 /**
  * NormalizedEvent — the durable envelope for all events flowing through
- * the system. Today: in-process EventEmitter. Tomorrow: NATS JetStream.
+ * the system. Mirrors oo.events.v1.Envelope in packages/shared-types/events/.
  *
  * Subject taxonomy:
  *   signals.task.synced      — Todoist (or other source) task list refreshed
@@ -10,10 +10,16 @@
  *   signals.integration.token_expired — OAuth token needs reconnect
  */
 export interface NormalizedEvent<T = unknown> {
+  /** UUID assigned by bus on publish */
+  eventId: string;
   /** NATS-style subject: domain.entity.verb */
   subject: string;
   /** ISO 8601 timestamp */
-  ts: string;
+  occurredAt: string;
+  /** "v1" — bump for breaking payload changes; see packages/shared-types/events/ */
+  schemaVersion: 'v1';
+  /** e.g. "services/api" */
+  producer: string;
   /** Monotonically increasing sequence number (in-process ring; JetStream seq in prod) */
   seq: number;
   payload: T;