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/cli/src/commands/task.ts

@@ -912,7 +912,7 @@ export async function runTaskImportFromGitHub(
   const importedUrls = new Map<string, string>();
   for (const task of existingTasks) {
     // Match Source URL anywhere in description (more robust than end-of-string anchor)
-    const sourceMatch = task.description.match(/Source: (https:\/\/github\.com\/[^\/]+\/[^\/]+\/issues\/\d+)/);
+    const sourceMatch = task.description.match(/Source: (https:\/\/github\.com\/[^/]+\/[^/]+\/issues\/\d+)/);
     if (sourceMatch) {
       importedUrls.set(sourceMatch[1], task.id);
     }