refactor: fix and tighten mechanical lint rules

- no-useless-escape: drop needless backslashes in character classes and
  URL/path regexes (gh-cli, store, task, modelFilter, useFileMention,
  RoutineEditor, ScheduleForm).
- no-case-declarations: wrap case bodies in ProjectOverview and
  SettingsModal with block scopes.
- prefer-const: convert a never-reassigned slug binding in agent-import;
  annotate legitimate forward-declared let bindings in dashboard.ts that
  callbacks close over before assignment.
- no-fallthrough: add missing break after settings-subcommand error.
- no-empty-interface/no-empty-object-type: convert ProjectManifest from
  empty interface extension to a type alias.
- no-unused-expressions: replace `x && x.method()` short-circuits in
  TerminalModal with optional chaining.

Then ratchet these rules from warn → error so regressions are blocked.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/ProjectOverview.tsx

@@ -108,12 +108,13 @@ export function ProjectOverview({
         case "name":
           comparison = a.project.name.localeCompare(b.project.name);
           break;
-        case "activity":
+        case "activity": {
           const aTime = a.project.lastActivityAt || a.health?.lastActivityAt || a.project.updatedAt;
           const bTime = b.project.lastActivityAt || b.health?.lastActivityAt || b.project.updatedAt;
           comparison = new Date(bTime).getTime() - new Date(aTime).getTime();
           break;
-        case "status":
+        }
+        case "status": {
           const statusOrder: Record<ProjectStatus, number> = {
             errored: 0,
             initializing: 1,
@@ -122,6 +123,7 @@ export function ProjectOverview({
           };
           comparison = statusOrder[a.project.status] - statusOrder[b.project.status];
           break;
+        }
       }
 
       return sortDirection === "asc" ? comparison : -comparison;