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>

tasks.md

@@ -56,7 +56,7 @@ Sizes: **S** = under a day, **M** = 1–3 days, **L** = 3–7 days.
 ### UI (HTMX + Tailwind)
 
 - [x] **P1-23** (M) Base layout, login page, session-aware nav
-- [ ] **P1-24** (M) Dashboard: host cards (status dot, last backup, repo size)
+- [x] **P1-24** (M) Dashboard: fleet summary tiles + host table (status dot + row accent + os/arch + last backup + repo size + snapshots + alerts + tags + run-now). Backed by `GET /api/hosts` + `GET /api/fleet/summary` (JSON) and a server-rendered HTML view. Empty state hands the operator the install command. HTMX `Run now` button posts to `/hosts/{id}/run-backup`.
 - [ ] **P1-25** (M) Host detail page: snapshots tab + run-now button
 - [ ] **P1-26** (M) Live job log viewer (WS-driven, auto-scroll, cancel button)
 - [ ] **P1-27** (M) "Add host" flow: form takes hostname + repo URL/username/password, mints token (TTL 1h), shows the operator a copy-friendly install command **and** a one-click "download preconfigured installer" — a `install-<hostname>.sh` with `RM_SERVER` + `RM_TOKEN` already templated in (cf. UrBackup Internet-mode push installer). Encrypted repo creds ride on the token row and get pushed to the agent on first WS connect (see secrets/keyring task).