fix(symbols): codepoint dump — chunked IPC, work-sized deadline, resumable stamp

A cold sync stamped 303 of 8,302 public symbols (3.6%) and reported 'ok':
the dump's lockstep protocol paid a full pipe round trip per symbol
(~100ms under load → ~10 symbols/s) against a fixed 30s wall clock, and
partial coverage logged at info.

- Pipeline stdin writes in chunks of 256 (worker replies in input order;
  both directions fit the pipe buffer) — round-trip cost per chunk, not
  per symbol; deadline sized to the work (max(120s, 50ms/name)) as a pure
  hang guard.
- Stamp is resumable: outside forceRefresh it only dumps rows with NULL
  codepoints, so an interrupted run converges next sync instead of
  re-walking the catalog; partial coverage now warns loudly with the
  deficit.
- Version reporting: the cache dir was named from the CDN URL's
  cache-buster ('SF-Symbols-8.dmg?2' → '8.2') while the log used the real
  bundle version (8.0); the dir is renamed to the bundle version so path,
  manifest, and log agree.