v0.11.1 — the syntax gate no longer fails open

Two real bugs in the post-write syntax check (P1.1's gate), found chasing a CI
flake rather than by reading code.

A timeout made the gate fail OPEN. The check ran with timeout=3 and swallowed
TimeoutExpired into "can't check", which the caller treats as permission to write.
That is right when the checker isn't installed and a hazard when it merely timed
out: node --check is ~0.02s warm but a cold start on a loaded machine is not, so
the gate reported "fine" on a file it had never checked and let invalid JS land.
Now 10s (FORGE_SYNTAX_TIMEOUT) plus one doubled retry; a genuine hang still reads
as "cannot check", never as "fine".

The error named a file that does not exist. The check runs on a temp copy, so its
error cites the temp path, rewritten back to the real basename — but tempfile
returns /var/folders/… while macOS reports /private/var/folders/…, so the replace
matched only the suffix and stranded the prefix: '/privatea.js:1' instead of
'a.js:1'. The model was being sent to fix the wrong file. Nothing covered it,
which is how a user-facing message stayed wrong unnoticed.

Both now pinned by tests. 725 tests, green on 3.10–3.13.