P1-24: live dashboard — fleet summary tiles + host table

Server-rendered HTML view backed by:
  - new store.FleetSummary aggregating host counts + repo bytes +
    snapshot total + open alerts + last-24h job rollup in two queries.
  - GET /api/hosts (JSON list of hosts in the dashboard projection).
  - GET /api/fleet/summary (JSON aggregate, same shape as above).

The HTML page (web/templates/pages/dashboard.html) renders the four
summary tiles + host table directly from store data — no separate
fetch. Per-row state colour comes from .host-row.{degraded,failed,
offline} which paint a 3px left edge so problem hosts are scannable
without reading. HTMX is loaded into the base layout so per-row
"Run now" buttons can hx-post to /hosts/{id}/run-backup, a thin
HTML wrapper that funnels into a new dispatchJob helper shared
with the JSON /api/hosts/{id}/jobs endpoint.

Empty state (zero hosts) collapses to the "no hosts yet" prompt
with the + Add host CTA — matches the v1 mockup.

Template helpers (internal/server/ui/funcs.go) added for byte
formatting (412 GB / 3.7 TB), relative time (3m ago / 2d ago), and
comma grouping (1,847). Pure Go, no template-magic dependency.

Browser-verified end-to-end with seeded fixture data: five hosts
across all four states render with correct dots, accents, last-
backup pills, sizes, snapshot counts, alerts, tags, and the right
action button (Run now / Retry / Run first / View → / offline).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/server/ui/ui.go

@@ -88,6 +88,7 @@ func New() (*Renderer, error) {
 		"templates/layouts/base.html",
 		"templates/layouts/chromeless.html",
 		"templates/partials/nav.html",
+		"templates/partials/host_row.html",
 	}
 
 	pageEntries, err := fs.Glob(web.FS, "templates/pages/*.html")
@@ -101,7 +102,8 @@ func New() (*Renderer, error) {
 	r := &Renderer{pages: make(map[string]*template.Template, len(pageEntries))}
 	for _, p := range pageEntries {
 		base := strings.TrimSuffix(path.Base(p), ".html")
-		t, err := template.New(base).ParseFS(web.FS, append(append([]string{}, commonPaths...), p)...)
+		t, err := template.New(base).Funcs(funcMap()).
+			ParseFS(web.FS, append(append([]string{}, commonPaths...), p)...)
 		if err != nil {
 			return nil, fmt.Errorf("ui: parse %s: %w", p, err)
 		}