Input History, Skills & ACP Enhancements

✨ New Features

• Input history navigation: use the Up/Down keys to quickly browse message history; fixed keyboard event crashes and cursor position issues
• File tree and Commit tab remain usable when there is no active session (no longer stuck)
• Prompt enhancement pipeline: restored pure-model prompt enhancement with cancel support
• Skills overhaul: skill management views, sidebar entry, detail modal, styling, and localization

🔌 ACP & Protocol

• JSON serialization validation for prompt payloads
• @file references sent as embeddedContext resource blocks

🛠 Bug Fixes & Stability

• Fixed "agent instance not found" with automatic session reload