42 - #1500

Reviewed at 822953d0ce2acdb12e0d9e9643dfb3fdbabd6efa. Approving — this is a pure
reorganization and I was able to prove that rather than assume it.

It converges on the existing majority style rather than inventing one. main already has
13 .f.mjs modules carrying their @imports inside the @module header block, including
fjs/media/json/parser/module.f.mjs from #1499. AGENTS.md documents @import usage but not
placement, so there was no rule to check against — the relevant question was which pattern the
repo already leans on, and this moves toward it.

The change is semantically inert. The risk worth taking seriously with this edit is a
@import quietly failing to resolve in its new position and the affected type silently
widening to any, which tsc will not always shout about. Diffing the emitted declarations
against main across the whole tree gives 0 type-alias differences and 0 const-signature
differences, so every published signature is exactly what main produces. Nothing degraded.

Backing that up at the source level: of the 21 changed files, 15 are token-identical to
main once comments are normalized away — as they must be, since only comment blocks moved.
The other 6 are the ones where imports are real syntax rather than comments (five .f.ts
proofs plus crypto/sign/proof.f.mjs), and normalizing import order and quote style shows all
six are unchanged in substance — no statement added, removed, or altered.

crypto/sign/proof.f.mjs also switches its specifiers from double to single quotes, which
matches both the rest of that file and the repo at large; no double-quoted specifiers remain in
any changed file.

Everything else. npx tsc --noEmit 0, npm run prepack 0 errors from a clean tree,
npm test 2368 pass / 0 fail against main's 2368, broken markdown links 144 on both sides,
branch level with origin/main. No CHANGELOG entry, which I think is right — the surface is
provably byte-identical, so there is nothing to tell a consumer.

One aside, explicitly not a request: crypto/sign/proof.f.mjs has no @module header. That
predates this PR — it previously opened straight into import { utf8 } — so nothing regressed
here, but it is now the one file in this set whose leading block is @import-only.