feat: enrich stage foundation — provider config, env setup, schema fix

- Remove foreign key on run_status.source_id to support sentinel rows
  for tracking one-time pipeline steps (compile_candidates, compile_votes,
  merge, compare)
- Add stage-3-enrich/config.ts with all provider configurations,
  ALL_PROVIDERS ordered local-first, and validateProviderKey() for
  startup key checks
- Add .env.example with required API keys for OpenRouter and Anthropic
- Add pipeline:run script to package.json using --env-file .env
- Add .env to root .gitignore coverage for data-pipeline/.env

data-pipeline/package.json

@@ -8,7 +8,8 @@
     "db:init": "tsx db/init.ts",
     "annotate": "tsx stage-2-annotate/scripts/annotate.ts",
     "test": "vitest run",
-    "test:watch": "vitest"
+    "test:watch": "vitest",
+    "pipeline:run": "tsx --env-file .env pipeline.ts"
   },
   "dependencies": {
     "@lila/shared": "workspace:*",