feat(ui): the Symbol view — callers, gutter-ported source, line-anchored callee rail (CG-44)

The core screen of `codegraph ui`: who calls a symbol on the left, its
verbatim body in the middle with a port on every line that has an outgoing
edge, and what it calls on the right — each callee row placed beside the line
that makes the call, with a hairline connector between them.

The callee rail is the part that is not a list. A row wants to sit at the
centre of its first call-site line and is pushed down only when that would
collide with the row above, so the rail keeps source order; the connector
still runs to the real line, so the displacement is visible rather than
silent. Positions come from measuring the laid-out DOM, so they are
recomputed on resize, on font load and whenever a fold opens.

Honesty is carried in the drawing, not in a footnote: a filled port means the
resolver matched something on that line and a hollow one means it only
guessed; uncertain connectors are dashed and their targets fold away behind
their count; synthesized edges are dashed differently and tagged with the
mechanism that made them; references that leave the index are text with a
soft underline rather than links to nowhere, and they are counted. Long
bodies keep their head plus a window round every call site — windowed on
graph edges only, since a function calling `console.log` two hundred times
would otherwise window round every line and buy nothing. Containers over 80
lines show a members outline with per-member fan-in/fan-out instead of 700
lines of braces.

Two small additions to the read-only API this needed:

* `/api/node` gives every outline member its own fanIn/fanOut (two batched
  queries for the whole outline). A class's own fan-out is nearly always
  zero because its methods do the calling, so without these the outline
  cannot say which member carries weight.
* `/api/stats` gains `blastScale` — the denominator the blast bar is drawn
  against, so one symbol's radius reads as wide or narrow *for this repo*.
  It is measured across the index's 24 most-depended-on symbols (found with
  a new `getTopDependedOn`, distinct dependents rather than edges), memoised
  against the index stamp, and reported as sampled; a symbol wider than the
  sample becomes the scale instead of overflowing the track.

Verified against a real index in a real browser: parity with the prototype on
`CodeGraph.sync` (259 lines, 27 callee rows, no overlaps), `GraphTraverser`
(20-member outline), a 773-line function (26 windows, 78 connectors), light
and dark, hover linking in both directions, keyboard-only navigation, and
reflow on resize and on fold toggles.

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

ui/src/App.svelte

@@ -10,13 +10,16 @@
   import NotFoundView from './views/NotFoundView.svelte';
   import { router, navigate, back, mapHref, flowHref } from './lib/router.svelte';
   import { trail } from './lib/trail.svelte';
+  import { project } from './lib/project.svelte';
 
-  // Filled by the project stats call once the JSON API exists (CG-42); the
-  // top bar renders nothing rather than a placeholder until then.
-  let project = $state<string | null>(null);
-  let stats = $state<string | null>(null);
   let query = $state('');
 
+  // One `/api/stats` for the whole app: the top bar's counts and the Symbol
+  // view's blast-radius denominator come out of the same payload.
+  $effect(() => {
+    void project.ensure();
+  });
+
   let topbar: TopBar | null = $state(null);
 
   let route = $derived(router.route);
@@ -81,7 +84,7 @@
 
 <svelte:window {onkeydown} />
 
-<TopBar bind:this={topbar} bind:query {project} {stats} />
+<TopBar bind:this={topbar} bind:query project={project.name} stats={project.summary} />
 <TrailBar />
 <main>
   {#if route.view === 'symbol'}
@@ -95,7 +98,7 @@
   {:else if route.view === 'unknown'}
     <NotFoundView path={route.path} />
   {:else}
-    <HomeView {project} />
+    <HomeView project={project.name} />
   {/if}
 </main>