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/core/src/agent-companies-types.ts

@@ -59,7 +59,7 @@ export interface AgentManifest extends AgentCompaniesFrontmatter {
   instructionBody?: string;
 }
 
-export interface ProjectManifest extends AgentCompaniesFrontmatter {}
+export type ProjectManifest = AgentCompaniesFrontmatter;
 
 export interface TaskManifest extends AgentCompaniesFrontmatter {
   assignee?: string;

packages/core/src/gh-cli.ts

@@ -173,13 +173,13 @@ export function ensureGhAuth(): void {
  */
 export function parseRepoFromRemote(remoteUrl: string): { owner: string; repo: string } | null {
   // HTTPS: https://github.com/owner/repo.git or https://github.com/owner/repo
-  const httpsMatch = remoteUrl.match(/github\.com\/([^\/]+)\/([^\/\.]+)(?:\.git)?$/);
+  const httpsMatch = remoteUrl.match(/github\.com\/([^/]+)\/([^/.]+)(?:\.git)?$/);
   if (httpsMatch) {
     return { owner: httpsMatch[1], repo: httpsMatch[2] };
   }
 
   // SSH: git@github.com:owner/repo.git or git@github.com:owner/repo
-  const sshMatch = remoteUrl.match(/github\.com:([^\/]+)\/([^\/\.]+)(?:\.git)?$/);
+  const sshMatch = remoteUrl.match(/github\.com:([^/]+)\/([^/.]+)(?:\.git)?$/);
   if (sshMatch) {
     return { owner: sshMatch[1], repo: sshMatch[2] };
   }

packages/core/src/store.ts

@@ -65,7 +65,7 @@ function assertSafeAbsolutePath(path: string): void {
     !isAbsolute ||
     path.startsWith("-") ||
     // Reject shell metacharacters, quotes, control chars, and NULs.
-    /["'`$\n\r\t;&|<>()*?\[\]{}\\\0]/.test(
+    /["'`$\n\r\t;&|<>()*?[\]{}\\\0]/.test(
       path.replace(/^[A-Za-z]:/, ""), // ignore the drive-letter colon on Windows
     )
   ) {