fix(skills): discover linked workspace skill directories

[hetaoBackend]

Change

Workspace Skills were silently omitted when .agents/skills, .claude/skills, or .minimax/skills was a directory symlink, or when an individual Skill directory linked outside its source root. Opt the configured compatibility sources into directory-link resolution and watch linked directories even before SKILL.md exists. Source enable settings and duplicate-name priority remain in effect; generic bounded roots and the rejection of SKILL.md file symlinks are unchanged.

Add 13 regression cases covering linked roots and children, relative and absolute targets, duplicate aliases, source disabling, link retargeting, live creation/edits, invalid links, and bounded-root behavior. Document the supported layouts.

Validation

• The initial regression run reproduced 8 failures; all 13 cases pass after the fix.
• PASS: VITEST_MAX_WORKERS=2 pnpm verify on clean commit eaf23caf046fd82a66d376bf4cdfeaafba83f4a7, macOS arm64 / Node 26.4.0, full profile: 14 gates passed (185.8 seconds), including 170 capability files / 4,549 passing tests.
• Built CLI offline smoke: combined .agents/skills and .claude/skills root aliases with a child link outside the workspace; confirmed the linked Skill appears in the model request and the CLI exits successfully. Uses a local synthetic provider with external network access denied.
• An initial full run with four workers timed out in the new Skill watcher test and an existing theme watcher test. Both passed in isolation. The new test now waits for an observed native watcher event before the one-shot Skill creation; final verification uses two workers.
• Performance: basic; no perf:full classification applies.
• NOT RUN: local Linux/Windows execution, live providers, and release/package installation. Remote CI is pending.

Publication and contribution checks

• Changes are contributed under the existing applicable licenses; no imported material or license changes.
• No credentials, account data, real user content, internal source history, or private review material is included.
• The new synthetic test was reviewed, declared in test/vitest-suites.json, and recorded by regenerating release/public-source.json.
• Capability documentation is updated. Offline fixtures are not described as live-service acceptance.

Maintainer handoff

Publication scope or license changes: none.

Shared-source port: pending.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}