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/dashboard.ts

@@ -366,8 +366,12 @@ export async function runDashboard(port: number, opts: { paused?: boolean; dev?:
   const dashboardStartedAt = Date.now();
 
   // Declare store and agentStore early so callbacks can safely reference them
-  // (they're assigned after initialization, but the variables exist from the start)
+  // (they're assigned after initialization, but the variables exist from the start).
+  // prefer-const disabled: callbacks close over these identifiers before the
+  // single assignment below, which requires `let` even though no reassignment occurs.
+  // eslint-disable-next-line prefer-const
   let store: TaskStore | undefined;
+  // eslint-disable-next-line prefer-const
   let agentStore: AgentStore | undefined;
 
   if (isTTY) {