feat: add session persistence, state management commands, and --new-tab click (#184)

Rebased and fixed implementation of PR #184 features on current main:

Session persistence:
- --session-name flag and AGENT_BROWSER_SESSION_NAME env var auto-save/restore
  cookies and localStorage across browser restarts
- State files stored in ~/.agent-browser/sessions/ with owner-only permissions
- AES-256-GCM encryption via AGENT_BROWSER_ENCRYPTION_KEY env var
- Auto-expiration of old state files (AGENT_BROWSER_STATE_EXPIRE_DAYS, default 30)

State management commands:
- state list: list saved state files with metadata
- state show <file>: display state summary (cookies, origins, domains)
- state rename <old> <new>: rename state files
- state clear [name] [--all]: clear saved states
- state clean --older-than <days>: delete expired states

New --new-tab flag for click command:
- Opens link href in a new tab instead of navigating the current tab

Security hardening:
- Session name validation prevents path traversal (CLI + daemon)
- safeHeaderMerge prevents prototype pollution in header merging
- WebSocket stream server binds to 127.0.0.1 only
- State files written with 0o600 permissions

Fixes applied over the original PR:
- Use color.rs module instead of hardcoded ANSI escape codes
- Align CLI output field names with daemon response format
- Add CLI-level --session-name validation (not just daemon-side)
- Avoid adding "DOM" to tsconfig.json lib (use proper typing in evaluate)
- Keep version at 0.9.3 (matches current main)
- Centralize session name validation in daemon.ts helper
- Update all documentation (README, SKILL.md, docs site, --help output)

Co-authored-by: Chris Tate <chris@ctate.dev>

docs/src/app/commands/page.mdx

@@ -149,8 +149,19 @@ agent-browser trace stop [path]       # Stop and save trace
 agent-browser console                 # View console messages
 agent-browser errors                  # View page errors
 agent-browser highlight <sel>         # Highlight element
-agent-browser state save <path>       # Save auth state
-agent-browser state load <path>       # Load auth state
+```
+
+## State management
+
+```bash
+agent-browser state save <path>       # Save auth state to file
+agent-browser state load <path>       # Load auth state from file
+agent-browser state list              # List saved state files
+agent-browser state show <file>       # Show state summary
+agent-browser state rename <old> <new> # Rename state file
+agent-browser state clear [name]      # Clear states for session name
+agent-browser state clear --all       # Clear all saved states
+agent-browser state clean --older-than <days>  # Delete old states
 ```
 
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