feat(memory): add explicit paths config for memory search

Add a `paths` option to `memorySearch` config, allowing users to
explicitly specify additional directories or files to include in
memory search.

Follow-up to #2961 as suggested by @gumadeiras — instead of auto-following
symlinks (which has security implications), users can now explicitly
declare additional search paths.

- Add `memorySearch.paths` config option (array of strings)
- Paths can be absolute or relative (resolved from workspace)
- Directories are recursively scanned for `.md` files
- Single `.md` files can also be specified
- Paths from defaults and agent overrides are merged
- Added 4 test cases for listMemoryFiles

src/config/types.tools.ts

@@ -226,6 +226,8 @@ export type MemorySearchConfig = {
   enabled?: boolean;
   /** Sources to index and search (default: ["memory"]). */
   sources?: Array<"memory" | "sessions">;
+  /** Additional paths to include in memory search (directories or .md files). */
+  paths?: string[];
   /** Experimental memory search settings. */
   experimental?: {
     /** Enable session transcript indexing (experimental, default: false). */