feat: git push status indicator + multi-select bulk push

- DB migration v2: git_pushed_at column on incidents
- markIncidentPushed(id): stamps the push timestamp
- loadGitConfig(): shared helper in lib/git.ts, removes duplication
- Home screen: colored dot per incident (red=never pushed,
  orange=dirty/modified after push, green=up to date);
  dot visible only when git is configured
- Home screen: long-press enters selection mode, tap toggles;
  action bar with Select unpushed / Select all shortcuts +
  bulk push with sequential progress counter
- [id].tsx: marks incident pushed after successful push,
  updates local state without reload

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

types/incident.ts

@@ -11,6 +11,7 @@ export interface Incident {
   createdAt: string;
   updatedAt: string;
   tags: string[];
+  gitPushedAt: string | null;
 }
 
-export type IncidentDraft = Omit<Incident, "id" | "createdAt" | "updatedAt">;
+export type IncidentDraft = Omit<Incident, "id" | "createdAt" | "updatedAt" | "gitPushedAt">;