feat(ui): entry points — routes, executable files and tests as flow starting points (CG-54)

`#/entry` answers "where does anything start" at full length, and turns any row
that names a symbol into a flow.

Server. `/api/entrypoints` gains `frameworks` (from `getDetectedFrameworks`), a
`tests` list, a `routes` limit of its own, and a cache keyed on the index build
— nothing here is read from disk, so unlike `/api/source` a cached answer cannot
be stale about drift. `routes.items` is now a `WireList` like every other list on
the payload.

Routes carry where the URL is REGISTERED as well as where it is served:
`getRoutingManifest` selects the route node's id, file and line, and
`buildRoutes` splits the verb off the name against a fixed list (never "the
first word", which would take the head off a file-routed `/blog/[slug]`). All
four payroll-go routes register in one router file and three are served from
another — group by the handler file and one router becomes two groups plus an
orphan.

`isTestFile` is split into `isTestPath` (test filename and directory
conventions) + the non-production catch-all, byte-identical at every existing
call site. The Tests list uses the narrow half: an example, a benchmark or a
fixture is off-target for ranking but is not a test, and a heading that says
"Tests" must not quietly count them. Tests rank by REACH — distinct other files
touched — because Go, Rust and Java put test work inside functions where a
module-level-calls ranking sees nothing. Two read-only engine queries make that
affordable: `getFileReachCounts` (the mirror of `getFileDependentCounts`, driven
from `nodes` by path so the cost follows the files asked about rather than the
edge table) and `getFileNodes`.

Viewer. `ui/src/lib/entry-model.ts` folds the four lists into file groups —
pure, and `panel.rows` stays exactly the sections it draws. `EntryView` +
`EntrySection` render them with the caller rail's `.filegroup` / `.row` shapes
rather than a second visual language for the same idea. A row that names a
callable symbol carries a `Flow ›` chip; the other end is typed or picked with
`→ here` on another row. File and test rows carry none: `/api/flow` searches by
name, and a file has none the path finder can look up.

A project with fewer than three resolvable routes gets no Routes heading at all,
not an empty one. Typing into the search box now also returns matching entry
points under their own heading below the symbol matches, so a URL comes back
with its handler attached; rows already in the results are dropped.

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

__tests__/ui-server-api.test.ts

@@ -973,12 +973,12 @@ export default app;
 
       expect(body.routes.routed).toBe(true);
       expect(body.routes.routeCount).toBe(4);
-      const urls = body.routes.items.map((e: any) => e.url);
+      const urls = body.routes.items.items.map((e: any) => e.url);
       expect(urls).toEqual(
         expect.arrayContaining(['GET /users', 'GET /users/:id', 'POST /users', 'DELETE /users/:id'])
       );
       // A route row has to be navigable, or it is a label.
-      expect(body.routes.items.every((e: any) => e.handlerId)).toBe(true);
+      expect(body.routes.items.items.every((e: any) => e.handlerId)).toBe(true);
     });
 
     it('honours the limit and says when it cut the list', async () => {
@@ -1118,7 +1118,7 @@ describe('GET /api/entrypoints', () => {
   it('says a project without routes is not routed rather than failing', async () => {
     const body = await getJson('/api/entrypoints');
     expect(body.routes.routed).toBe(false);
-    expect(body.routes.items).toEqual([]);
+    expect(body.routes.items.items).toEqual([]);
     expect(body.routes.routeCount).toBe(0);
   });