feat(ui): the whole file — full source with gutter ports and intra-file call arcs (CG-52)

The File view gains a Source tab: the file itself, top to bottom, with the
Symbol view's line grid, gutter ports and call-site links, a line-anchored
callee rail, and — in the left margin — an arc for every call that stays inside
the file, drawn from the calling line to the callee's definition line.

The arcs are the point. Source order is already a layout, chosen by whoever
wrote the file, so a file's internal call structure can be drawn with no
algorithm placing anything. Crabviz's idea, in the one place it is legible.

Everything is arithmetic, not measurement. The Symbol view queries the laid-out
DOM to place a callee row beside its line; a 6 820-line file cannot afford that.
Here a line is exactly 20px at `10 + (n - 1) x 20`, so ~90 line elements exist at
a time and the arcs, ports, rail rows and connectors are all functions of a line
number. `src/mcp/tools.ts` scrolls at a 16.6ms median frame.

- `GET /api/filecode/<path>` — outline, one call group per (caller, callee) PAIR
  with its call-site lines, unresolved references, and the file's length. The
  source is NOT in it: it pages through `/api/source` 800 lines at a time with a
  discarded 150-line lead-in, so a page starting inside a block comment does not
  render prose as code, and so the ports and arcs are complete from the first
  frame while the text fills in behind them.
- `intraFileCalls` is counted over the groups actually returned, so the header
  and the picture under it cannot disagree once a cap bites.
- Above 40 arcs the diagram narrows to the symbol under the pointer (or the one
  the scroll position is inside) and the header states the total. Accent is for
  the pointer only, never for the filter.
- Sticky outline rail at >= 1400px, following the reader down the file.
- `QueryBuilder.getUnresolvedReferencesInFile` — one indexed lookup instead of
  one per symbol; `buildOutlineEntries` lifted out of `/api/file` so both
  readings of a file draw the same rows.

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

site/src/content/docs/guides/viewer.md

@@ -42,6 +42,14 @@ The viewer never presents a guess as a fact:
 
 Clicking any file path opens the **file view**: everything that file depends on, its outline in source order, and everything that depends on it.
 
+## The whole file
+
+The **Source** tab on that screen replaces the outline with the file itself, top to bottom, with the same gutter markers and the same right-hand list of what each line calls — a 6,800-line file scrolls as smoothly as a 60-line one, and the text pages in behind you.
+
+The margin on the left is the part you cannot get anywhere else: **an arc for every call that stays inside the file**, drawn from the calling line to the line the callee is defined on. Source order is the only layout — nothing is placed by an algorithm, because the author already placed it — so the shape of a file's internal call structure is legible at a glance. Hover a line to light the arcs the function under your cursor takes part in; click an arc to jump to the other end. On a file with more than forty of them the diagram narrows to the symbol you are reading rather than drawing a wash of overlapping sweeps, and the count stays in the header.
+
+A rail on the far left lists the file's symbols and follows you as you scroll, when the window is wide enough for it.
+
 ## The flow
 
 Type **"how does execute reach getFile"** into the search box — or `execute -> getFile` — and the first result opens the **Flow** strip: the call path between the two symbols, left to right, one card per hop.