feat(skills): improve descriptions with routing logic

Apply OpenAI's recommended pattern for skill descriptions:
- Add 'Use when' conditions for clear triggering
- Add 'NOT for' negative examples to reduce misfires
- Make descriptions act as routing logic, not marketing copy

Based on: https://developers.openai.com/blog/skills-shell-tips/

Skills updated:
- coding-agent: clarify when to delegate vs direct edit
- github: add boundaries vs browser/scripting
- weather: add scope limitations

Glean reported 20% drop in skill triggering without negative
examples, recovering after adding them. This change brings
Clawdbot skills in line with that pattern.

skills/coding-agent/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: coding-agent
-description: Run Codex CLI, Claude Code, OpenCode, or Pi Coding Agent via background process for programmatic control.
+description: "Delegate coding tasks to Codex, Claude Code, or Pi agents via background process. Use when: (1) building/creating new features or apps, (2) reviewing PRs (spawn in temp dir), (3) refactoring large codebases, (4) iterative coding that needs file exploration. NOT for: simple one-liner fixes (just edit), reading code (use read tool), or any work in ~/clawd workspace (never spawn agents here). Requires PTY mode."
 metadata:
   {
     "openclaw": { "emoji": "🧩", "requires": { "anyBins": ["claude", "codex", "opencode", "pi"] } },

skills/github/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: github
-description: "Interact with GitHub using the `gh` CLI. Use `gh issue`, `gh pr`, `gh run`, and `gh api` for issues, PRs, CI runs, and advanced queries."
+description: "GitHub operations via `gh` CLI: issues, PRs, CI runs, code review, API queries. Use when: (1) checking PR status or CI, (2) creating/commenting on issues, (3) listing/filtering PRs or issues, (4) viewing run logs. NOT for: complex web UI interactions (use browser), bulk operations across many repos (script with gh api), or when gh auth is not configured."
 metadata:
   {
     "openclaw":

skills/weather/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: weather
-description: Get current weather and forecasts (no API key required).
+description: "Get current weather and forecasts via wttr.in or Open-Meteo. Use when: user asks about weather, temperature, or forecasts for any location. NOT for: historical weather data, severe weather alerts, or detailed meteorological analysis. No API key needed."
 homepage: https://wttr.in/:help
 metadata: { "openclaw": { "emoji": "🌤️", "requires": { "bins": ["curl"] } } }
 ---