Admin dashboard: pages, Lane observability, poll pass log, per-Series intervention (#134) (#148)

Spec #134, all ten tickets. Closes #134.

## What ships

The admin surface becomes four bookmarkable addresses behind one nav row, and Lane observability stops dying with the process.

- **#138** `/admin` splits into Overview, Lanes, Readers, Series, each a real route with the active tab underlined.
- **#139** `poll_passes` and `poll_lanes` land as durable tables with their store surface.
- **#140** cross-Series admin read model, with the privacy boundary in the projection: the Reader id that raised a Latest Chapter never leaves the store package.
- **#141** the poller records exactly one pass row per exit, with a skip reason and outcome counts.
- **#142** Series list: eight hygiene filters, Site and Library narrowing, paging — all of it in the query string, so a filtered list is a bookmark.
- **#143** Overview: a three-state verdict line and a stats block where every non-zero figure links to the list that counts it.
- **#144** per-Series detail page, keyed by the `site:series_id` composite the rest of the system already uses.
- **#145** the Lanes page reads the database; the in-memory Lane state, `web.LaneReporter` and `latest.Status` are deleted.
- **#146** Forced Poll: *Check now* stamps `series.force_poll_at` and never commands the poller.
- **#147** pause and resume one Site's Lane, with a mandatory 1h/6h/24h expiry.

## Shape of the design

Two decisions carry the rest. **Commands go through the database, never at the poller**: both *Check now* and a Lane pause write a row the next pass reads, so they survive a restart and the whole surface stays testable with no poller running. And **pending is derived, never stored** — the request stamp being newer than the check stamp — which self-clears on the check stamp with no second write and no sweeper, because the check stamp is written before the fetch.

ADRs: `docs/adr/0012-persisted-lane-state.md`, `docs/adr/0013-commands-through-the-database.md`.

## Verification

`go test ./...` green on the merged base (`264839e`), all packages, Docker-backed. `gofmt -l` and `go vet` clean.

Every ticket was reviewed on both axes (`cr-spec` + `cr-standards`) before merge.

## Known, non-blocking

- **#143** the verdict ignores never-reported Lanes when other Lanes have reported, and the per-Site table lists Sites that have Series rather than the whole registry. The ticket prose asks for eight hygiene figures per Site; the design mock and the landed `.tbl.sites` grid both say six columns, and the mock won.
- **#146** two `SeriesPage` scans per press instead of a keyed read — `ponytail:`-commented in-tree with the upgrade path.
- **#147** a paused Site with no pass row yet renders no row and so no control, since the Lanes page lists Sites that have passed.
- **#141** a sibling browser Lane declining at the top of a pass records as `sidecar-down`. Specified deliberately; the later spec in this series settles it.

Reviewed-on: #148
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/internal/latest/sites.go

@@ -401,9 +401,10 @@ const (
 	// express (docs/research/cloudflare-bot-scoring-and-poll-cadence.md);
 	// below it the Lane is outrunning its own plan and says so loudly.
 	minGap = time.Second
-	// refuseBackoff is how long a Lane waits after its Site refused twice in
-	// one run before attempting it again.
-	refuseBackoff = 15 * time.Minute
+	// RefuseBackoff is how long a Lane waits after its Site refused twice in
+	// one run before attempting it again. Exported so the web layer can derive
+	// browser reachability from the pass log over the same window (issue #145).
+	RefuseBackoff = 15 * time.Minute
 	// browserWakeCount and browserWakeAge gate a browser Lane's run: five or
 	// more due Series, or any one of them waiting this long, or Chrome stays
 	// asleep (ADR-0005 on-demand browser).
@@ -511,6 +512,18 @@ var sites = map[string]site{
 	},
 }
 
+// SiteNames returns every registry Site, sorted. The admin Series list's Site
+// select needs the full registry, not just the Sites that have rows, and
+// laneNames() is the poller's copy of the same list — both read this.
+func SiteNames() []string {
+	names := make([]string, 0, len(sites))
+	for name := range sites {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	return names
+}
+
 // browserBackedSites is derived from the registry: the Sites whose pages are
 // read through the browser sidecar. Sorted so callers that range it (the
 // browser fetcher's dispatch) see a stable order instead of map-iteration