fix(proxy): preserve fetch semantics through the proxy adapter

Addresses review round 4 on #2099 — three posted comments and three suppressed
ones, all valid.

- A rebuilt Response reported `url: ""`, `redirected: false`, and
  `type: "default"` even after undici followed a redirect: a fetch-contract
  regression visible only to proxy users, and one `core/auth/endpointOverrides.ts`
  explicitly guards against by declining to rebuild at all. This adapter has no
  such choice — the response arrives from the wrong realm — so it now reinstates
  the three with `defineProperty`.

- Normalizing a `Request` input dropped every option the Request itself carried
  beyond method/headers/body/signal. Most visibly `redirect`: a
  `new Request(url, { redirect: "manual" })` started following redirects instead
  of surfacing them. All of them are now carried through, with an explicit
  `init` still winning per the fetch contract.

  Both are covered by tests driving a real redirect through a real proxy, and
  both were confirmed to fail without the fix.

- `@modelcontextprotocol/ext-apps` was added only to the CLI's `external` list.
  AGENTS.md requires every root-declared runtime dependency in all three, since
  which client reaches it is a function of what `core/` imports rather than of
  the client's own code. Added to the web runner and TUI lists too.

- The `BUNDLED_CLIENTS` test compared the hard-coded list against a hard-coded
  copy of itself, so a new tsup-bundled client would have left it green while
  going unchecked. It now discovers clients from disk (a client is tsup-bundled
  iff it ships a tsup config) and compares. Verified it fails when a stub client
  is added.

- AGENTS.md's project tree still described `core/mcp/node/` as only the stdio
  transport factory; it now carries `proxyFetch.ts` and its role.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JTHVxSu8AUgHRLvo1ntZ8H
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/cli/tsup.config.ts

@@ -39,10 +39,10 @@ export default defineConfig({
     "@modelcontextprotocol/client",
     "@modelcontextprotocol/core",
     // Root-declared and reached through `core/mcp/apps.ts`, so it must be
-    // external here like every other root runtime dependency — it was being
-    // inlined (dragging the transitive v1 SDK and zod-to-json-schema with it),
-    // which the #2067 guard surfaced. ESM, so it was not failing the way
-    // `undici` did; the rule is what it violated.
+    // external here like every other root runtime dependency (AGENTS.md). This
+    // client was actually inlining it — dragging the transitive v1 SDK and
+    // zod-to-json-schema in with it — which the #2067 guard surfaced. ESM, so it
+    // was not failing the way `undici` did; the rule is what it violated.
     "@modelcontextprotocol/ext-apps",
     "commander",
     "pino",