fix(ingestion): bump mcp-chassis to v0.7.1; label refused REST requests by route

1. Rejections are logged. chassis v0.2.0 refused without a log line, so
   since #149 an unknown REST caller got silent 401s. v0.7.1 writes
   `mcp auth rejected` (reason, remote, token fingerprint, path) and
   `mcp auth accepted` per authenticated request. Tested through
   buildMux.

2. Fallout: since chassis v0.7 (mcp-chassis#4) NewJWTValidator no longer
   fails on OIDC discovery; the issuer resolves lazily and a JWT gets
   503-and-retry until it does. #83's boot retry loop therefore never
   retried, and its tests failed. buildJWTValidator now builds once and
   logs an issuer still unresolved at boot. Behaviour change: a
   misconfigured issuer no longer exits the process; JWTs get 503, the
   static bearer keeps working. internal/startupretry is now unused.

3. Metrics: authenticated REST requests were already labelled by route
   (the REST mux sets Pattern on the same *http.Request the middleware
   reads). Requests refused by auth never reached the REST mux and were
   labelled path="/". labelRESTPattern now sets the REST route's pattern
   before auth; unmatched paths keep "/", so the label set stays bounded.

Closes #155

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/go.mod

@@ -51,7 +51,7 @@ require (
 )
 
 require (
-	git.d-ma.be/mathias/mcp-chassis v0.2.0
+	git.d-ma.be/mathias/mcp-chassis v0.7.1
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 // indirect
 	github.com/goccy/go-json v0.10.3 // indirect