fix(skills): detect built-in skills from all npm install layouts

[taoyizhi68]

Problem

Settings → Skill Management showed Built-in Skills (0) — "No built-in skills detected" even though the gateway was happily loading all 52 skills and chats worked fine.

Root cause: the skills:list IPC handler in desktop/src/main.ts and getSkillSourceDirs() in desktop/src/skill-integrity.ts hard-coded the built-in skills directory to only two paths — the legacy deployer layout under ~/.openclaw-node/:

~/.openclaw-node/node_modules/openclaw/skills
~/.openclaw-node/lib/node_modules/openclaw/skills

Per the updated install flow described in CLAUDE.md, the deployer now installs Node.js via the official MSI to %ProgramFiles%\nodejs\ (or reuses a system Node ≥22.16), and openclaw is installed via npm i -g, which lands the package in:

• %AppData%\npm\node_modules\openclaw\skills (per-user npm prefix — default on Windows)
• %ProgramFiles%\nodejs\node_modules\openclaw\skills (per-machine)
• %LocalAppData%\Programs\nodejs\node_modules\openclaw\skills (per-user Node)

None of these were probed by the UI's skill-listing code, so the panel rendered empty.

Notably resolveOpenClawEntry() in path-resolver.ts already handled the %AppData%\npm layout — which is why the gateway found openclaw.mjs and ran normally; only the UI list was blind.

Fix

Add a shared resolveBuiltinSkillsDir() helper in desktop/src/path-resolver.ts that mirrors the candidate list used by resolveOpenClawEntry():

1. Packaged app resources (process.resourcesPath/openclaw/skills)
2. ~/.openclaw-node/node_modules/openclaw/skills (classic deployer)
3. ~/.openclaw-node/lib/node_modules/openclaw/skills (lib deployer)
4. %AppData%/npm/node_modules/openclaw/skills (per-user npm global)
5. %ProgramFiles%/nodejs/node_modules/openclaw/skills (per-machine Node)
6. %LocalAppData%/Programs/nodejs/node_modules/openclaw/skills (per-user Node)

Returns the first existing path, falling back to candidate #2 (legacy layout) so log messages stay informative when nothing is installed yet.

Both call sites — skills:list in main.ts and getSkillSourceDirs() in skill-integrity.ts — now route through this helper.

Verification

• All 32 tests in path-resolver.test.ts + skill-integrity.test.ts pass.
• Updated skill-integrity.test.ts to also mock resolveBuiltinSkillsDir.
• Local run with npm run dev confirms the file-watcher picks up the right directory:

  Watching skill directory: C:\Users\<user>\AppData\Roaming\npm\node_modules\openclaw\skills
  

• Settings → Skill Management now lists all 52 built-in skills instead of "No built-in skills detected".

Files changed

• desktop/src/path-resolver.ts — new resolveBuiltinSkillsDir()
• desktop/src/main.ts — skills:list uses the helper
• desktop/src/skill-integrity.ts — getSkillSourceDirs() uses the helper
• desktop/src/skill-integrity.test.ts — mock updated