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/package.json

@@ -15,7 +15,9 @@
     "test": "vitest run",
     "test:watch": "vitest",
     "type-check": "tsc --noEmit",
-    "clean": "rm -rf dist"
+    "clean": "rm -rf dist",
+    "buf:lint": "buf lint events",
+    "buf:breaking": "buf breaking events --against '.git#branch=main,subdir=packages/shared-types/events'"
   },
   "devDependencies": {
     "@vitest/coverage-v8": "^4.1.4",