feat: skill builder UI, daemon lifecycle, update notifications

[initializ-mk]

Summary

• Skill Builder UI: Interactive LLM-powered skill creation wizard with real-time chat, YAML frontmatter validation, and one-click save to agent config
• Daemon Lifecycle: Agents now run as forge serve daemon processes via exec.Command instead of in-process goroutines — agents survive UI shutdown and are detected on restart via .forge/serve.json + TCP probe
• Update Notifications: Dashboard checks GitHub Releases API (30-min cache) and shows an animated "Update Available" banner when a newer version exists
• Version Display: Sidebar footer shows current Forge version and link to useforge.ai
• Install Script: One-line curl | bash installer/upgrader at repo root
• Code Review Skills: diff, file, standards, and github review skills
• Codegen Skills: React and HTML code generation embedded skills
• A2A Auth: Bearer token authentication for A2A server
• Documentation: Updated dashboard docs with skill builder section, installation docs with install script

Test plan

• cd forge-ui && go test ./... — all tests pass
• cd forge-cli && go test ./... — all tests pass
• Start UI → start an agent → verify it shows as running
• Stop UI (Ctrl+C) → verify agent is still running
• Restart UI → verify agent shows as running (detected by scanner)
• Stop agent from UI → verify it stops
• Skill Builder: open chat, generate a skill, validate, save
• Update banner appears when running an older version