feat: improve session resume reliability and persist user settings

- Filter empty sessions from history API (check for conversation content)
- Add --resume fallback to new session if resume fails (prevents dead panes)
- Pass resumeSessionId through respawnPane for dead pane recovery
- Persist respawn presets and runMode to server settings (cross-device sync)
- Fix mobile touch handling for Recent Sessions dropdown (DOM API + touch CSS)

src/mux-interface.ts

@@ -75,6 +75,8 @@ export interface RespawnPaneOptions {
   claudeMode?: ClaudeMode;
   allowedTools?: string;
   openCodeConfig?: OpenCodeConfig;
+  /** Resume a previous Claude conversation when respawning */
+  resumeSessionId?: string;
 }
 
 /**