core: keep recordings when the Permission Model blocks fsync - #1907

CI pins Node 26.7.0. On Windows, the Node run of the Yoga default-config
worker test sometimes crashed with an access violation at process exit.
A minidump showed the fault inside Node, not OpenTUI: after a worker
exits, Node 26.7.0 can write one byte into the freed worker Realm, and
here that byte broke V8's page pool, which then crashed in
`V8::Dispose`. No OpenTUI code was loaded at the time. Node fixed this
in nodejs/node#65778, released in 26.10.0.

This pins the current LTS, 26.13.0, in every workflow that pinned
26.7.0. It needed #1907 first: since Node 26.9.0, `FileHandle.sync()`
throws under the Permission Model, which the core Node lane uses, and
that broke audio recording. The `engines` floor stays at `>=26.4.0`.

Tested on Linux under 26.13.0 with the core and Solid Node lanes and the
core, Solid, SSH and Keymap packed-consumer tests; on Windows, this PR's
CI and later runs are the evidence. The crash hit about 1 in 175 Windows
jobs, so one green run proves little.

Take 9b7b1ba (core: keep recordings when the Permission Model blocks
fsync, anomalyco#1907). Since Node 26.9.0, FileHandle.sync() throws
ERR_ACCESS_DENIED whenever the Permission Model is on
(nodejs/node#65431). AudioRecorder finalized a recording with sync() and
close(), so under --permission every recording failed with "Audio
recorder finalize failed" and was discarded. OpenTUI's own Node test lane
runs with --permission and hits this as soon as CI moves past Node 26.7.

The recorder now closes the file without the sync when that call is
denied, then publishes it as usual. Any other sync error still fails the
recording and keeps the destination. The audio capture docs say that
under --permission the file is not forced to disk before the rename.
packages/core/src/audio.ts, the existing sync-failure rows in
packages/core/src/tests/audio.test.ts, and
packages/docs/application-apis/audio-capture.mdx are the three files.
The incoming commit deletes nothing. The local side deletes nothing.
Merge-tree was clean. This does not push to anomalyco/opentui and does
not create origin/master.