refactor: give the autofixer one shared module for PM2 execution, data paths and app loading

[atomantic]

Summary

autofixer/ is two PM2-managed processes — server.js (the repair loop) and ui.js (the dashboard) — that carried byte-identical copies of the same plumbing: PM2_BIN resolution, the execPm2 promise wrapper, the DATA_DIR / APPS_FILE / AUTOFIXER_DIR / INDEX_FILE constants, and loadApps(). The Windows rationale for resolving PM2's JS entry point rather than launching through pm2.cmd (which flashes a console window) was documented once in each copy, so a fix would have had to land twice.

Both processes now import a new package-local autofixer/shared.js:

• One copy of PM2_BIN, execPm2 and the Windows rationale comment.
• Paths resolved from shared.js's own location, so the two processes cannot disagree about which data/ directory they read.
• One loadApps().
• server.js keeps its own PROVIDERS_FILE, SETTINGS_FILE, SESSIONS_DIR and WORKTREES_DIR — only the subset ui.js also needed moved.

The module stays package-local rather than importing server/services/pm2.js, which has an equivalent execPm2: that import would drag the whole server dependency graph into a package whose package.json declares only express. Behavior is unchanged — the extracted code is verbatim, and the now-unused spawn / createRequire / fileURLToPath imports were dropped from the consumers.

autofixer/shared.test.js pins the three things a runtime-only failure would otherwise hide: PM2_BIN still resolves to an existing bin/pm2 (a PM2 package-layout change would otherwise surface only on the next repair attempt), every path anchors to the package-sibling data/ directory, and loadApps() falls back to [] rather than throwing. Node resolves pm2 by walking node_modules upward from autofixer/, which needs the root install — CI runs npm ci --prefix server only, and server/node_modules is never on that path — so the suite self-skips when pm2 is unresolvable instead of failing there. Both branches were exercised locally.

Test plan

• cd server && npm test — 1880 files / 37883 tests pass (this runner globs ../autofixer).
• npx vitest run ../autofixer/ — 3 files / 34 tests pass, including the 5 new ones.
• Skip path verified by temporarily pointing the guard at an unresolvable package: Test Files 1 skipped (1) / Tests 5 skipped (5), no import error.
• node --check on both rewritten consumers; import('./autofixer/shared.js') smoke-loaded and its export surface confirmed.
• No changelog entry: .changelog/README.md forbids per-branch fragments.

Notes

The configured local reviewer (ollama, gemma-4-12B-coder-fable5-composer2.5) returned 400 ... does not support thinking — the known failure tracked in #5960 — so the required review is inconclusive, not clean. This PR is intentionally left unmerged pending that review.

Closes #5732

https://claude.ai/code/session_01SQQHNCXHxrXNaJ4FEk8N23

[atomantic]

Required code review was not completed before publication. This PR is intentionally left open and will not be merged until the required review completes.