fix(server): detect file changes inside untracked directories on refresh

[chuks-qua]

What

file.refresh fingerprinted git status --porcelain, which collapses untracked directories into a single ?? dir/ line. Adding or removing a file inside an already-untracked directory never moved the dirty-set fingerprint, so files.changed never broadcast and cached @ file autocomplete stayed stale across attention refreshes.

The refresh now runs git status --porcelain --untracked-files=all, expanding untracked directories to per-file entries — the same granularity file.list already uses via git ls-files --others --exclude-standard. Ignore rules, the bounded single-status-call design, and per-scope baselines are unchanged.

Verified end to end on the live worktree runtime: public WS file.refresh baseline → external write of verify1735/alpha.ts inside a new untracked dir → files.changed{changedPaths:["verify1735/alpha.ts"]} push (removal too). In the real web app, reopening the @ picker after an external write shows the new file without a restart (screenshots attached).

Why

Closes #1735. Users directing agents hit stale file autocomplete when an agent or external tool creates files inside a new directory; the cached list silently missed them even after reopening the picker.

UI Changes

Behavioral fix with UI evidence attached: before, the @ picker lacks verify1735-ui/beta.ts; after an external write plus one attention refresh, the reopened picker lists it.

Review Notes

• Regression suite (audit-untracked-file-refresh.test.ts) uses real git against temp repos: add, remove, nested dirs, unchanged set, ignored files, staging (?? f → A f intentionally stays silent, matching single-file staging), and status.showUntrackedFiles=no override. Red-before/green-after confirmed against the audit's pinned reproduction.
• New ws-events tests pin the consumer side: files.changed clears the autocomplete cache and bumps the diff revision for both thread and workspace scopes.
• Known pre-existing edge, slightly amplified: execFile's 1 MiB maxBuffer can make refresh return null on repos with huge unignored untracked trees. list() shares the exposure; not introduced here.

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