feat(ui): the File view — outline in source order between two dependency rails (CG-46)

Clicking a file path now opens the file itself: what reaches into it, its
symbols in source order, and what it reaches.

The two rails count DEPENDENCIES, not import statements. The prototype drew
`imports` edges; on this repo `src/graph/traversal.ts` imports two files and
depends on four, because it reaches the LRU cache through a call no import
names. A rail headed "Imports 2" would be quietly wrong about what changing the
file would touch, which is the only question the screen answers — so the rails
read `getFileDependencies` / `getFileDependents` and merge the import rows in
for the symbol names. Imports that resolved to nothing indexed keep their own
section rather than vanishing.

The outline is windowed above 250 rows against a fixed 28px row: this repo's
own fixtures hold a 1,681-symbol `.d.ts`, and paging it would hide the one
thing an outline is for. `src/mcp/tools.ts` draws its 135 rows whole.

`/api/file` gains `topLevel.calls` — module-level calls out of the file node —
so a file that RUNS something offers the badge that opens it as a symbol, the
only place code belonging to no symbol can be read.

File results in the search palette and the entry-point list now land here
rather than on the file node's Symbol view.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

__tests__/ui-server-api.test.ts

@@ -845,6 +845,17 @@ describe('GET /api/file/<path>', () => {
     expect(body.dependencies).toContain('src/types.ts');
   });
 
+  it('says whether the file runs anything at its top level', async () => {
+    // `src/main.ts` instantiates a Service and calls two functions outside
+    // every definition — code no outline row can show, because it belongs to
+    // no symbol. `src/cache.ts` only defines things.
+    const main = await getJson('/api/file/src/main.ts');
+    expect(main.topLevel.calls).toBeGreaterThanOrEqual(2);
+
+    const cache = await getJson('/api/file/src/cache.ts');
+    expect(cache.topLevel.calls).toBe(0);
+  });
+
   it('404s a file that is not in the index and refuses one outside the project', async () => {
     const missing = await getStatusAndJson('/api/file/src/nope.ts');
     expect(missing.status).toBe(404);