Centralize git/GitHub runtime state into WorkspaceGitService

Consolidate workspace git watch lifecycle, background fetch scheduling,
and GitHub PR polling from session.ts and BackgroundGitFetchManager into
a single daemon-scoped WorkspaceGitService. Sessions now subscribe to
the service for push-driven updates instead of coordinating watchers and
fetch intervals themselves. Workspace payloads gain optional gitRuntime
and githubRuntime fields for richer client-side display.

packages/server/src/server/worktree-session.ts

@@ -95,7 +95,7 @@ type RegisterPendingWorktreeWorkspaceDependencies = {
 
 type CreatePaseoWorktreeInBackgroundDependencies = {
   paseoHome?: string;
-  emitWorkspaceUpdateForCwd: (cwd: string, options?: { dedupeGitState?: boolean }) => Promise<void>;
+  emitWorkspaceUpdateForCwd: (cwd: string) => Promise<void>;
   sessionLogger: Logger;
   terminalManager: TerminalManager | null;
 };