web: git.sr.ht-style dashboard and unified nav brand

Adopt the family look the dolt service already has. The nav brand
becomes circle icon + site name + red service label (dropping the
hub-origin variant), matching every other service on the instance. The
logged-in index turns into the two-column dashboard: a sidebar with the
service blurb and the jump form, and the repositories as shared-theme
event-list cards — name, visibility as small muted text (non-public
only, lowercase), description underneath. The big in-page h2 lives on
only for anonymous visitors, where the nav has no user context yet.

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.

web: http server, sourcehut chrome, compare/commit pages

Implement the compare.sr.ht HTTP layer over the committed core/gitx/authz
packages:

- Server assembly (New) from shared SourceHut config: [git.sr.ht] repos,
  [meta.sr.ht]/[compare.sr.ht] origins, [sr.ht] site-name/environment, and
  the hashed stylesheet resolved by globbing the embedded static FS.
- Routes: landing, repo page, compare (base..base...head, .patch escape
  hatch), single-commit (+.patch), embedded static assets, healthz. Compare
  form GET canonicalizes to a clean URL via 302.
- SourceHut chrome port to html/template: nav service switcher (canonical
  order, paste/pages/hub excluded, compare active), login/logout with
  return_to, environment banner.
- Embedded compare-data JSON (template.JS so html/template's script-context
  escaper leaves it verbatim; json.Marshal's HTML escaping blocks a
  </script> breakout) plus the vendored bundle.js scaffold.
- httptest coverage with a stub Authorizer and a real git-CLI fixture repo.

The cmd layer must wire, in order: RealIP, Recoverer, Logger,
config.Middleware(conf,"compare.sr.ht"), authz.Middleware.