refactor: Extract terminal rendering logic to useTerminalRenderer composable

- Create useTerminalRenderer.ts with all xterm.js logic
- Support custom theme, fontSize, fontFamily options
- Add handleReplay() for proper visibility handling
- Add getBufferContent() for copying terminal content
- Refactor FloatingTerminal.vue to use composable
- Refactor TerminalPage.vue to use composable
- Server: Add request-replay message type for on-demand replay
- Server: Remove auto-replay on connect (client requests when ready)
- Fix xterm.js rendering issues with hidden containers (v-show)

server/config.ts

@@ -7,7 +7,7 @@ export const WORKING_DIR = process.cwd().replace(/[\\\/]server$/, '')
 export const SHELL = process.platform === 'win32' ? 'powershell.exe' : 'bash'
 export const SHELL_ARGS = process.platform === 'win32' ? ['-NoLogo', '-NoProfile'] : []
 export const DEFAULT_SESSION_ID = 'main'
-export const MAX_BUFFER_LINES = 1000
+export const MAX_BUFFER_LINES = 10000
 
 // Database
 export const DB_PATH = 'agent-ui.db'