fix(explore): damp ambient declaration files on flow queries (CG-28)

A file that declares nothing but types and that nothing in the index depends
on — a hand-written ambient `.d.ts` of global shims, vendored typings, module
augmentation — cannot answer a flow question: no bodies, no call edges, no
behaviour, nothing typed by it. But the identifiers it declares are exactly the
generic ones a prose question uses (`Body`, `Message`, `ImageMetadata`,
`ReadableStream`), so on term overlap it out-scored the implementation. Measured
on the new fixture: rank #1 and 51% of delivered source, with the flow's own
entry file pushed out of the response entirely.

Measured first, per the issue: the Wrangler `worker-configuration.d.ts` that
opened this is already handled by CG-25's banner detection, worth 15-46 points
of envelope share across four flow queries. CG-25 credited; only the un-bannered
case needed anything.

`rankPenalty` now multiplies score and graph mass by 0.5 for such files, taken
as the STRONGER of it and the generated penalty rather than multiplied — one
property two signals see must not be charged twice. Detection is structural, not
by extension, and four conditions deep. Two of them were forced by measurement:
requiring every symbol to be type-level takes the corpus flag rate from 1-18%
(which swept in Kotlin sealed classes, Rust mod.rs re-exports and django's
locale tables) down to 0-4%; requiring that nothing depends on the file
separates an ambient shim from a working types module, and without it the rule
demoted displacement-ts's pipeline `types.ts` and broke the CG-31 gate.

A query that NAMES a declared type is exempt, so a question about a type still
reaches its declaration at full weight. Precise tokens only, so "…the file
body…" cannot exempt a `Body` interface it never meant to name; this needs its
own set because `namedSeedIds` is callable-only and a type never becomes one.

Regression evidence in docs/benchmarks/explore-declaration-only-cg28.md:
6-repo envelope sweep byte-identical against a clean baseline build, zero
ambient files reach the candidate set on VS Code across five queries, corpus
flag rate 0-0.74%, both allocation fixtures PASS, full suite 2,978 green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

__tests__/fixtures/ambient-decls-ts/src/lib/request.ts

@@ -0,0 +1,44 @@
+export interface ParsedUpload {
+  ok: true;
+  key: string;
+  body: ReadableStream<Uint8Array>;
+  contentType: string;
+  width: number;
+  height: number;
+  format: string;
+}
+
+export interface ParseFailure {
+  ok: false;
+  error: string;
+}
+
+/**
+ * Pull the object key, declared dimensions and the raw body stream off an
+ * upload request. Never buffers the body — the stream is handed straight to
+ * the storage layer.
+ */
+export async function parseUploadRequest(
+  request: Request,
+): Promise<ParsedUpload | ParseFailure> {
+  const url = new URL(request.url);
+  const key = url.searchParams.get('key');
+  if (!key) return { ok: false, error: 'missing key' };
+  if (!request.body) return { ok: false, error: 'missing body' };
+
+  return {
+    ok: true,
+    key,
+    body: request.body as ReadableStream<Uint8Array>,
+    contentType: request.headers.get('content-type') ?? 'application/octet-stream',
+    width: numberParam(url, 'width'),
+    height: numberParam(url, 'height'),
+    format: url.searchParams.get('format') ?? 'jpeg',
+  };
+}
+
+function numberParam(url: URL, name: string): number {
+  const raw = url.searchParams.get(name);
+  const parsed = raw ? Number.parseInt(raw, 10) : 0;
+  return Number.isFinite(parsed) ? parsed : 0;
+}