fix(httpauth): wildcard resource fallback, json.Number precision, xerrors JSON error bodies (#1)

ClaimsPermissionProvider.ResolveMask now falls back to the "*" resource key when the
exact resource is absent in the JWT masks claim. Specific resource takes precedence;
wildcard is the fallback. Enables ADMIN wildcard masks ({"*": MaxInt64}) to pass every
endpoint guard without per-resource entries.

Add json.Number handling alongside existing int64/float64 paths. json.Number is
produced by jwt.WithJSONNumber() (httpauth-jwt) and preserves math.MaxInt64 exactly —
float64 would round to 2^63 and overflow on cast back to int64.

Export WriteJSONError(w, status, code, message) — shared JSON error helper for all
httpauth-* provider packages. Ensures a consistent {"code":"...","message":"..."} body
and Content-Type: application/json across the full middleware stack.

AuthzMiddleware and EnrichmentMiddleware now use WriteJSONError with xerrors code
constants (UNAUTHENTICATED, PERMISSION_DENIED, INTERNAL) instead of http.Error which
writes text/plain. AuthzMiddleware also fixes a wrong code string: UNAUTHORIZED →
UNAUTHENTICATED (stable gRPC-aligned name, matching xerrors.ErrUnauthorized).

Add xerrors v1.0.1 as a direct dependency for the code constants.

Reviewed-on: #1
Co-authored-by: Rene Nochebuena Guerrero <rene@nochebuena.dev>
Co-committed-by: Rene Nochebuena Guerrero <rene@nochebuena.dev>

go.sum

@@ -1,2 +1,4 @@
 code.nochebuena.dev/go/rbac v1.0.0 h1:FnsU1HU6vvwchKuZNxDa9RPIFeNwJi0vShWvHKABMws=
 code.nochebuena.dev/go/rbac v1.0.0/go.mod h1:LzW8tTJmdbu6HHN26NZZ3HzzdlZAd1sp6aml25Cfz5c=
+code.nochebuena.dev/go/xerrors v1.0.1 h1:fgXoabY/ZwxAzaM1sKFf3sbL7ZHWyDxItB/rdbnl0mo=
+code.nochebuena.dev/go/xerrors v1.0.1/go.mod h1:03MMVfrhaf4XmTMgMrEUFCmuZPGHUCKDitiQvwCuwvY=