[codex] Make adapter sync non-destructive

[chiehwangs]

Summary

• Preserve local adapter overrides during install-time adapter sync instead of deleting changed official-site overrides.
• Convert stale adapter files, legacy shim files, and stale tmp lock files from automatic cleanup to detection-only warnings.
• Add an install-time safety regression test to prevent recursive or direct deletion APIs from returning to scripts/fetch-adapters.js.
• Make shell completion fast path validate manifest JSON before using it, so corrupt manifests fall back to full discovery instead of returning empty completions.

Root Cause

scripts/fetch-adapters.js ran during global install or explicit adapter sync and used recursive forced deletion plus direct file deletion against ~/.opencli. That could remove user adapter directories or files without an explicit per-item confirmation step.

A second issue was in hasAllManifests: it only checked that manifest files existed. If cli-manifest.json existed but contained invalid JSON, the fast completion path still ran and returned empty completions instead of falling back to full discovery.

Validation

• HOME="$PWD/.local-home" npx vitest run --project unit src/install-safety.test.ts
• HOME="$PWD/.local-home" npx vitest run --project unit src/completion-fast.test.ts
• HOME="$PWD/.local-home" npx vitest run --project unit
• HOME="$PWD/.local-home" npm run typecheck
• node --check scripts/fetch-adapters.js
• HOME="$PWD/.local-home" OPENCLI_FETCH=1 node scripts/fetch-adapters.js
• HOME="$PWD/.local-home" node dist/src/main.js hackernews top --limit 1 -f json