feat(ingestion): migrate to gitea.d-ma.be/mathias/mcp-chassis v0.1.0

Second port of the MCP chassis (gitea-mcp was first, commit 658f4ba).
Closes the chassis-adoption loop on the two highest-LOC consumers.

Changes:
- Drop ingestion/internal/auth/ entirely (jwt.go + jwt_test.go +
  protected_resource.go + protected_resource_test.go) — chassis provides
  JWTValidator + ProtectedResourceHandler with identical semantics.
- Drop ingestion/internal/mcp/auth.go (BearerAuth function, ~65 LOC)
  and the integration test auth_test.go (~200 LOC) — chassis
  BearerMiddleware replaces it. Static-Bearer-or-Dex-JWT precedence and
  RFC 9728 resource_metadata challenge behavior preserved 1:1.
- cmd/server/main.go: import chassis as `chassisauth`, rewire the three
  call sites. Use realm="brain" in the BearerMiddleware call so a 401
  challenge identifies the resource as the brain MCP.

OAuth client_credentials handler (ingestion/internal/oauth) stays —
chassis v0.1.0 covers only the JWT path; OAuth flow is a candidate for
chassis v0.2.0 once a second MCP needs it (rule of three).

Net delta: -~330 LOC of duplicated auth code; +1 import; +1 GOPRIVATE
env requirement on dev machines (documented in the spike handoff
2026-05-22-mcp-chassis-spike.md).

task check green (lint + test + vet + govulncheck).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ingestion/cmd/server/main.go

@@ -12,8 +12,9 @@ import (
 	"strings"
 	"time"
 
+	chassisauth "gitea.d-ma.be/mathias/mcp-chassis/auth"
+
 	"github.com/mathiasbq/hyperguild/ingestion/internal/api"
-	"github.com/mathiasbq/hyperguild/ingestion/internal/auth"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/llm"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/mcp"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/embed"
@@ -181,16 +182,13 @@ func main() {
 	mux.HandleFunc("POST /backfill-refs", h.BackfillRefs)
 	mux.HandleFunc("POST /backfill-embeddings", h.BackfillEmbeddings)
 	mux.HandleFunc("GET /pass-rate", h.PassRate)
-	var jwtValidator *auth.Validator
-	if dexURL := os.Getenv("DEX_ISSUER_URL"); dexURL != "" {
-		audience := os.Getenv("MCP_AUDIENCE")
-		v, err := auth.NewValidator(dexURL, audience)
-		if err != nil {
-			logger.Error("build jwt validator", "err", err)
-			os.Exit(1)
-		}
-		jwtValidator = v
-		logger.Info("jwt auth enabled", "issuer", dexURL)
+	jwtValidator, err := chassisauth.NewJWTValidator(ctx, os.Getenv("DEX_ISSUER_URL"), os.Getenv("MCP_AUDIENCE"))
+	if err != nil {
+		logger.Error("build jwt validator", "err", err)
+		os.Exit(1)
+	}
+	if jwtValidator != nil {
+		logger.Info("jwt auth enabled", "issuer", os.Getenv("DEX_ISSUER_URL"))
 	}
 
 	// Resource-metadata URL is only emitted on 401 when Dex OAuth is
@@ -200,13 +198,13 @@ func main() {
 	if dexURL := os.Getenv("DEX_ISSUER_URL"); dexURL != "" {
 		resourceURL := os.Getenv("MCP_RESOURCE_URL")
 		mux.HandleFunc("GET /.well-known/oauth-protected-resource",
-			auth.ProtectedResourceHandler(resourceURL, dexURL))
+			chassisauth.ProtectedResourceHandler(resourceURL, dexURL))
 		if resourceURL != "" {
 			resourceMetadataURL = strings.TrimRight(resourceURL, "/") + "/.well-known/oauth-protected-resource"
 		}
 	}
 
-	mux.Handle("/mcp", mcp.BearerAuth(mcpToken, jwtValidator, resourceMetadataURL, mcpSrv))
+	mux.Handle("/mcp", chassisauth.BearerMiddleware(mcpToken, jwtValidator, "brain", resourceMetadataURL, mcpSrv))
 
 	// Opt-in OAuth 2.0 client_credentials flow for claude.ai's custom-MCP
 	// integration UI, which has no static-Bearer field. Setting both