fix(electrobun): address all 20 Codex review findings

CRITICAL:
- PTY leak: Terminal.svelte now calls pty.close on destroy, not just unsubscribe
- Agent session cleanup: clearSession() removes done/error sessions, backend
  deletes after 60s grace period

HIGH:
- Clone branch passthrough: user's branch name flows through callback
- Circular imports: extracted rpc.ts singleton, broke main.ts ↔ App.svelte cycle
- Settings wired to runtime: Terminal reads cursor/scrollback from settings
- Security disclaimer: added "prototype — not system keyring" notice
- ThemeEditor: fixed basePalette → initialPalette reference

MEDIUM:
- Clone race: UUID suffix instead of count-based index
- Silent failures: structured error returns from PTY handlers
- WebKitGTK mount: only current + previous group mounted
- Debug listeners: gated behind DEBUG, cleanup on destroy
- NDJSON residual buffer parsed on process exit
- Codex adapter: deduplicated tool_call/tool_result
- extraEnv: rejects CLAUDE*/CODEX*/OLLAMA* keys
- settings-db: runMigrations() with version tracking
- active_group: persisted via settings.set

LOW:
- Removed dead demo code, unused variables
- color-mix() fallbacks added

ui-electrobun/src/mainview/ProjectCard.svelte

@@ -27,8 +27,8 @@
     cloneOf?: string;
     /** Max clones reached for this project. */
     clonesAtMax?: boolean;
-    /** Callback when user requests cloning. */
-    onClone?: (projectId: string) => void;
+    /** Callback when user requests cloning (receives projectId and branch name). */
+    onClone?: (projectId: string, branch: string) => void;
   }
 
   let {
@@ -78,7 +78,7 @@
       cloneError = 'Use only letters, numbers, /, _, -, .';
       return;
     }
-    onClone?.(id);
+    onClone?.(id, cloneBranchName);
     showCloneDialog = false;
   }