fix: serve RFC 9728 path-suffixed metadata, document connector redirect URIs

Two separate discovery footguns, both found while debugging an Authentik
"Redirect URI Error" on a claude.ai custom connector.

RFC 9728 §3.1 puts the metadata for a resource identified by
`https://host/api/mcp` at `/.well-known/oauth-protected-resource/api/mcp`.
Only the root form was served, so clients that derive the metadata URL from
the MCP endpoint URL — rather than reading `resource_metadata` off our 401 —
got Next.js's HTML 404 and failed discovery with a JSON parse error.

Add a `[...path]` route serving the same document with `resource` naming the
suffixed identifier (§3.3 has the client compare it as an exact string, so
echoing the bare origin would be rejected). The document body moves to
`lib/auth/resource-metadata.ts` so the two routes cannot drift apart on
`scopes_supported` — a divergence there costs you the `aud` claim or the
refresh token. Paths are allowlisted rather than wildcarded so this cannot
advertise resources the app does not serve. `buildWwwAuthenticate()` still
points at the root URL; this change is purely additive.

Separately, the redirect URIs an MCP provider needs depend on how clients
reach it: a loopback URI for the CLI, `https://claude.ai/api/mcp/auth_callback`
for a claude.ai custom connector. Registering only the former is what produces
the "Redirect URI Error" page, and a portless `http://localhost/callback`
entry matches nothing the CLI sends. Document both, keyed on the literal
error text, and note that DCR is enterprise-gated on Authentik so these are
hand-registered on a FOSS instance.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

terraform/README.md

@@ -72,6 +72,16 @@ The redirect URI you register on the Web UI client is
 `https://${domain_name}/api/auth/callback/oidc`, so plan the domain name
 *before* configuring the IdP.
 
+The MCP client needs its own list, and most of it does not depend on the
+domain: a loopback URI for the Claude Code CLI, plus
+`https://claude.ai/api/mcp/auth_callback` if anyone will add the server as a
+claude.ai custom connector. Only the manual-paste fallback,
+`https://${domain_name}/auth/cli-callback`, follows the domain. See
+[Which redirect URIs to register](../README.md#which-redirect-uris-to-register)
+— a client can only register its own redirect URI against an IdP that offers
+Dynamic Client Registration, which Authentik gates behind an enterprise
+licence, so plan on adding all of these by hand.
+
 ---
 
 ## Quick start