phase 2 (part 4): SSE stream via io.Pipe, OIDC JWT auth middleware

- SSE stream: GET /events/stream using io.Pipe to bridge the SSE
  goroutine to the response body. Replay from Last-Event-ID via
  in-memory broker with DB fallback. LISTEN/NOTIFY fan-out to all
  subscribers. Heartbeat every 15s. Bounded channels.
- OIDC JWT auth: validates Bearer tokens against Authentik/OIDC
  issuer via JWKS discovery + key caching. Extracts sub/email into
  context actor. Falls back to static bearer tokens. Dev mode (no
  OIDC + no tokens) = open.
- Config: OIDCIssuer, OIDCClientID env vars
- SSE + OIDC infrastructure complete, build passes, all tests pass

Remaining: MCP server, conformance tests, wire audit middleware

go.sum

@@ -17,6 +17,8 @@ github.com/go-openapi/swag/jsonname v0.25.5 h1:8p150i44rv/Drip4vWI3kGi9+4W9TdI3U
 github.com/go-openapi/swag/jsonname v0.25.5/go.mod h1:jNqqikyiAK56uS7n8sLkdaNY/uq6+D2m2LANat09pKU=
 github.com/go-openapi/testify/v2 v2.4.0 h1:8nsPrHVCWkQ4p8h1EsRVymA2XABB4OT40gcvAu+voFM=
 github.com/go-openapi/testify/v2 v2.4.0/go.mod h1:HCPmvFFnheKK2BuwSA0TbbdxJ3I16pjwMkYkP4Ywn54=
+github.com/golang-jwt/jwt/v5 v5.3.1 h1:kYf81DTWFe7t+1VvL7eS+jKFVWaUnK9cB1qbwn63YCY=
+github.com/golang-jwt/jwt/v5 v5.3.1/go.mod h1:fxCRLWMO43lRc8nhHWY6LGqRcf+1gQWArsqaEUEa5bE=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=