feat: add initial skill authoring workspace

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

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+# skill_lib
+
+Dedicated ZeroClaw-style skill library for SGClaw browser workflows.
+
+## Layout
+
+Runtime skill packages live under `skills/<name>/`.
+
+Each package should use this shape:
+
+```text
+skills/<skill-name>/
+├── SKILL.md
+├── references/
+├── assets/
+└── scripts/   # optional
+```
+
+## Package Contract
+
+- Required file: `SKILL.md`
+- Repository-standard frontmatter keys: `name`, `description`, `version`, `author`, `tags`
+- `description` must be trigger-oriented and concise
+- Keep `SKILL.md` focused on workflow and decision rules
+- Put long operational detail into `references/`
+- Put preserved source artifacts, templates, or snapshots into `assets/`
+- Add `scripts/` only when deterministic repeated work should not be re-described in prose
+- For browser extraction tasks, prefer a packaged deterministic script before generic browser probing
+- Treat the structured artifact as the primary output contract for downstream skills
+- Encode blocked/login/captcha failure semantics explicitly instead of collapsing them into "no data"
+
+## Authoring Guidance
+
+Use [BROWSER_SKILL_AUTHORING.md](./BROWSER_SKILL_AUTHORING.md) when creating or
+updating browser-facing skills. It captures the concrete rules learned from the
+live Zhihu hotlist extraction failure and recovery.
+
+## Scope
+
+This repository stores skill packages, not Rust runtime code. Runtime dispatch, browser transport, and persistence implementations stay in their original source repositories.
+
+## Verification
+
+See [VERIFY.md](./VERIFY.md) for the repository-level validation checklist and expected structure checks.