feat: /healthz reports JWT validator status (refs #6)

/healthz now returns JSON with three-state JWT status: disabled
(DEX_ISSUER_URL unset), enabled (validator initialized), or
degraded (configured but init failed — only static-token auth
currently accepted). last_error surfaces the init failure so ops
can correlate with Dex outage windows.

Partial fix for #6. The cited internal/auth/jwt.go moved out
of this repo in 658f4ba (mcp-chassis migration); per-attempt
logging and 503 + WWW-Authenticate temporarily_unavailable
require chassis-side changes and a coordinated v0.1.1 bump
across all MCP consumers — tracked separately.

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

cmd/gitea-mcp/healthz.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+type healthStatus struct {
+	OK  bool      `json:"ok"`
+	JWT jwtStatus `json:"jwt"`
+}
+
+// jwtStatus surfaces the runtime state of the Dex JWT validator so ops
+// can distinguish "Dex unreachable at startup" from "JWT auth not
+// configured" — both previously degraded silently to static-token-only
+// (refs hyperguild/gitea-mcp#6).
+type jwtStatus struct {
+	// Status is one of: "disabled" (DEX_ISSUER_URL not set),
+	// "enabled" (validator initialized), "degraded" (configured but
+	// init failed; only static-token auth currently accepted).
+	Status    string `json:"status"`
+	LastError string `json:"last_error,omitempty"`
+}
+
+func newHealthzHandler(dexConfigured, validatorReady bool, initErr error) http.HandlerFunc {
+	status := healthStatus{OK: true, JWT: jwtStatus{Status: jwtStatusFor(dexConfigured, validatorReady)}}
+	if initErr != nil {
+		status.JWT.LastError = initErr.Error()
+	}
+	body, _ := json.Marshal(status)
+	return func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write(body)
+	}
+}
+
+func jwtStatusFor(dexConfigured, validatorReady bool) string {
+	switch {
+	case !dexConfigured:
+		return "disabled"
+	case validatorReady:
+		return "enabled"
+	default:
+		return "degraded"
+	}
+}