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>

CHANGELOG.md

@@ -22,6 +22,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - A generated CRUD or protobuf layer no longer crowds out the hand-written code sitting beside it: generated files are now recognized by the `// Code generated by … DO NOT EDIT.` style banner written at the top of the file, not just by a filename that looks generated. Re-index after upgrading to pick up the new detection. (#1500)
 - Test and spec files in a repository's top-level `test/` or `spec/` directory are now recognized as such, so they no longer take room from the code you asked about. (#1500)
 - Generated type-declaration files that announce themselves with a "Generated by … by running …" banner — Cloudflare Wrangler's `worker-configuration.d.ts` is the common one — are now recognized as generated. Previously a file like that could take most of a `codegraph_explore` answer on nothing more than a few common words, pushing the hand-written code you asked about out of the response entirely. Re-index after upgrading to pick up the new detection.
+- A hand-written type-declaration file — an ambient `.d.ts` of global shims, vendored typings, module augmentation — no longer takes over a `codegraph_explore` answer about how something works. Files like these declare common names (`Body`, `Message`, `ImageMetadata`) and nothing else, so a plainly-worded question could match one strongly enough that it ranked first and crowded the actual handler out of the answer. They are now ranked lower for questions about behaviour, and are still listed by name so one follow-up call fetches them. Asking about a type by name still returns its declaration first, and a shared types module the rest of your code imports is unaffected.
 - A CodeGraph process that gets force-killed — by the stuck-process watchdog, a crash, or the OS — no longer leaves the database's write-ahead log behind to grow without bound. Previously each killed session stacked more data onto the same log file and nothing ever shrank it, which on machines where sessions were killed regularly could quietly eat tens of gigabytes of disk. The log is now capped, and any oversized leftover is reclaimed automatically the next time the project is opened. Thanks @tiendungdev for the exceptional Windows report that pinned this down. (#1431)
 - The background server's watchdog no longer kills a healthy server that is just waiting on a slow disk: like indexing already does, it now checks whether the database files are still making progress before concluding the process is stuck. Fewer spurious kills also means fewer leftover write-ahead logs. (#1431)
 - `codegraph status` now shows the write-ahead log's size next to the database size and warns when killed sessions have left it oversized, and every line in the background server's log now carries a timestamp so kills and restarts can be placed in time. (#1431)