chrome: the head links from ecore, and no shipped favicon

layout.html hardcoded <link rel="icon" href="/static/logo.svg">, and
web/static/logo.svg was this service's copy of the brand circle chrome
now inlines as a data: URI. Both go: the head renders srht-head-links,
which emits the stylesheet and the icon guarded on emptiness, and the
icon costs no request and cannot 404.

The static tree is two hashed artefacts now, so the arm of
TestStaticBundleAndCSS that asserted an hour-cacheable unhashed asset has
nothing left to ask about; TestFaviconIsInline takes its place and also
pins that the data: URI reaches the page rather than #ZgotmplZ.

web: add long-line wrapping toggle

web: hide the per-row diff scrollbar gutter (overlay style)

Each @pierre/diffs code row scrolls horizontally on its own
(overflow-x: scroll) and reserves a classic scrollbar track sized to the
measured --diffs-scrollbar-gutter. On platforms with non-overlay
scrollbars (e.g. macOS "always show"), that track shows as a grey strip
under any row with a long line, reading as leftover bottom padding.

Set --diffs-scrollbar-gutter-override: 0 on #diff-root so the track is
never reserved; long lines stay scrollable by trackpad / wheel. Verified
the override wins over a simulated 14px measured gutter (reserved height
stays 0).

Re-hashed the embedded stylesheet.

web: remove grey padding bands inside each diff file

Two sources put a grey strip above the first line and below the last,
inside the file border:

- The shared `base` partial's `section { padding-bottom: .5rem }` applied
  to .diff-file (it is a <section>). Cancel it with padding-bottom: 0.
- The @pierre/diffs vertical code padding (--diffs-gap-block, default 8px)
  above the first and below the last line. Set it to 0 on #diff-root; it
  inherits into the DIFFS-CONTAINER shadow DOM. Horizontal code padding
  (--diffs-gap-inline) is left on its default.

Re-hashed the embedded stylesheet.

web: tighten diff and file-tree spacing

Address three spacing complaints in the compare view:

- File tree: switch @pierre/trees to the "compact" density preset (24px
  rows, 0.8 factor) so folder/child rows read as a dense index rather
  than an airy list.
- Diff blocks: drop the inter-file gap (.diff-file margin-bottom
  1rem -> .5rem) and the tree/diff column gap (1rem -> .75rem).
- File tree height: size the mount to its content height (capped at the
  viewport) instead of always filling the viewport, removing the band of
  empty tree background below the last file. Re-measures on resize and on
  every tree change (expand/collapse) via tree.subscribe.

Rebuilt and re-hashed the embedded bundle and stylesheet.

web: content-hash the bundle and colour the status column

Two diff-view fixes reported against the deployed instance.

Empty file tree after an upgrade: bundle.js had a stable filename served with a
1-hour cache, so browsers kept a pre-fix bundle and the @pierre/trees sidebar
rendered blank. Content-hash the bundle like the stylesheet — Makefile emits
bundle.<sha256[:8]>.js, server.go globs it into a BundleHref, the templates
reference {{.BundleHref}}, and the hashed name is served immutable. A deploy now
always busts the cache.

Unreadable status column: the changed-files table rendered A/M/D in the dim
default cell colour, near-invisible on the dark chrome. Render each status as a
semantic .diff-status badge (added=green, modified=amber, deleted=red,
renamed=blue) with light/dark variants, via statusClass/statusLabel helpers and
a small self-contained style block (the sourcehut-derived main.min.css can't be
rebuilt locally).

Tests resolve the hashed bundle via a bundleName helper and assert its immutable
cache header; docs updated for the hashed filename.

web: full-width split diff view with a rendered file tree

Make the commit and compare pages full-bleed and default to the side-by-side
(split) diff, so the layout matches a conventional diff viewer: file tree on
the left, split diff on the right.

- layout.html renders the content wrapper with a per-page ContainerClass;
  chrome() defaults it to "container" and the commit/compare handlers set
  "container-fluid" for the diff views (the nav stays centered).
- app.ts defaults DEFAULT_LAYOUT to "split".
- Fix the @pierre/trees sidebar rendering blank: its virtualized container
  collapses to zero height unless the mount has a definite height, so
  sizeTreeRoot() gives #tree-root a viewport-height panel (re-applied on
  resize). Rebuilt the vendored bundle.

frontend: pierre diffs/trees bundle and sourcehut theme css

Vendored esbuild bundle (frontend/src/app.ts) rendering @pierre/diffs
FileDiff per file and a @pierre/trees FileTree sidebar against the SSR
#compare-data contract, plus scss/main.scss (base + compare views)
compiled and content-hashed into web/static/.