feat(security): add client-side skill security enforcement

Add a capability-based security model for community skills, inspired by
how mobile and Apple ecosystem apps declare capabilities upfront. This is
not a silver bullet for prompt injection, but it's a significant step up
from the status quo and encourages responsible developer practices by
making capability requirements explicit and visible.

Runtime enforcement for community skills installed from ClawHub:

- Capability declarations (shell, filesystem, network, browser, sessions)
  parsed from SKILL.md frontmatter and enforced at tool-call time
- Static SKILL.md scanner detecting prompt injection patterns, suspicious
  constructs, and capability mismatches
- Global skill security context tracking loaded community skills and
  their aggregate capabilities
- Before-tool-call enforcement gate blocking undeclared tool usage
- Command-dispatch capability check preventing shell/filesystem access
  without explicit declaration
- Trust tier classification (builtin/community/local) — only community
  skills are subject to enforcement
- System prompt trust context warning for skills with scan warnings or
  missing capability declarations
- CLI: `skills list -v`, `skills info`, `skills check` now surface
  capabilities, scan results, and security status
- TUI security log panel for skill enforcement events
- Docs updated across 7 files covering the full security model

Companion PR: openclaw/clawhub (capability visibility + UI badges)

docs/tools/creating-skills.md

@@ -35,11 +35,27 @@ description: A simple skill that says hello.
 When the user asks for a greeting, use the `echo` tool to say "Hello from your custom skill!".
 ```
 
-### 3. Add Tools (Optional)
+### 3. Declare Capabilities
+
+If your skill uses system tools, declare them in the `metadata.openclaw.capabilities` field:
+
+```markdown
+---
+name: deploy_helper
+description: Automate deployment workflows.
+metadata: { "openclaw": { "capabilities": ["shell", "filesystem"] } }
+---
+```
+
+Available capabilities: `shell`, `filesystem`, `network`, `browser`, `sessions`.
+
+Skills without capabilities are treated as read-only (model-only instructions). Community skills published to ClawHub **must** declare capabilities matching their tool usage — undeclared capabilities are blocked at runtime.
+
+### 4. Add Tools (Optional)
 
 You can define custom tools in the frontmatter or instruct the agent to use existing system tools (like `bash` or `browser`).
 
-### 4. Refresh OpenClaw
+### 5. Refresh OpenClaw
 
 Ask your agent to "refresh skills" or restart the gateway. OpenClaw will discover the new directory and index the `SKILL.md`.