Owner-only admin page: Reader roster plus Poll Lane status (#102) (#107)

Closes #102.

The only operational surface was /healthz and a fold-out roster inside the owner's own reading page. This adds /admin: an owner-only page carrying the Reader roster and one row per Poll Lane.

- **Poller seam.** `latest.Poller` records each Lane's last pass (`Site`, `Due`, `Checked`, `LastRun`, `Gap`, `Clamped`, `Browser`) and answers `LaneStatus()`; the page reads that snapshot, never a table. A pass that returns before computing its figures (refusal backoff, sidecar down) carries the previous pass's figures forward rather than recording zeroes, and a Lane that has never reached a pace renders no gap at all. Refusal and sidecar reachability are derived at snapshot time.
- **Owner gate at registration.** Every route reaching past the acting Reader lives in `adminRoutes()` and is wrapped in `requireOwner` when it is registered, so a missing gate is visible in the route list rather than hidden in a handler. `web.AdminPatterns()` is what the gate test walks, so a new route cannot be added without being tested. A non-owner gets 404, never 403.
- **Nil poller is a first-class state.** `main.newRouter` takes the reporter as an interface and converts a nil `*Poller` to a nil interface; no poller and no completed pass both render "No data yet" with the reason spelled out, rather than confident zeroes.
- **Roster moved** off the reading page onto /admin, with the Sighting counters and a confirm-gated `Clear marks` control. #103 fills those counters, so on delivery they read zero for everyone - deliberate ordering.
- **One accent, `--patina`** (verdigris, both colour branches): the far side of the wheel from ember's crimson and clear of the archive blue. Ember still means new chapter only; revocation still wears --danger.

Verification: `go vet ./...` and `go test ./...` green (Docker-backed); admin page screenshotted at 1100px and 390px in both colour schemes. Reviewed on both axes (spec, standards); findings on the accent hue, zero-figure honesty and three tests that could not fail are fixed in 58014eb.
Reviewed-on: #107
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/internal/latest/poller.go

@@ -57,6 +57,10 @@ type Poller struct {
 	mu            sync.Mutex
 	refuseUntil   map[string]time.Time
 	browserDownAt time.Time
+	// laneStates is the owner's page snapshot of each Lane's last pass
+	// (issue #102), keyed by Site. Guarded by mu; a Site appears only after
+	// its first pass, so a restart renders "no data yet" rather than zeroes.
+	laneStates map[string]LaneState
 	// coverWG tracks in-flight cover work. Covers heal in the background so a
 	// slow cover host cannot delay the next Series-page Poll; tests join it
 	// before asserting on cover fetches.
@@ -218,6 +222,10 @@ func (p *Poller) runOnce(ctx context.Context) {
 // production Lane's rate limit; the deterministic test entry runs back to back.
 func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.Duration {
 	now := p.Now()
+	// Snapshot this pass for the owner's page (issue #102). Recorded on every
+	// return path, with the figures filled in where the pass computes them.
+	st := LaneState{Site: name, LastRun: now, Browser: isBrowserSite(name)}
+	defer func() { p.recordLaneState(st) }()
 	if until := p.refusalBackoff(name); now.Before(until) {
 		// Cooling down after a refusal: do not attempt this Site at all.
 		return until.Sub(now)
@@ -238,18 +246,23 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 		// No fetcher at all right now (browser absent, no fallback): every
 		// Series stays unstamped and due, so a browser that appears after a
 		// restart finds its full queue waiting (issue #100).
+		st.Gap = defaultGap
 		return defaultGap
 	}
 
 	due, err := p.Store.DueForLatestCheck(name, now.Add(-s.Rest).UnixMilli())
 	if err != nil {
 		log.Printf("latest poll %s: due query: %v", name, err)
+		st.Gap = defaultGap
 		return defaultGap
 	}
+	st.Due = len(due)
 	if s.Browser != nil && f == p.BrowserFetch && !browserWakeDue(due, now, s.Rest) {
 		// Below both thresholds Chrome stays asleep (ADR-0005 on-demand
 		// browser): waking it for a single Poll would cost a challenge solve
-		// per request.
+		// per request. The Lane still paces at the default gap, which is what
+		// the owner's page must show rather than a zero.
+		st.Gap = defaultGap
 		return defaultGap
 	}
 	if s.Browser != nil {
@@ -265,9 +278,11 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 	eligible, err := p.Store.EligibleSeriesCount(name)
 	if err != nil {
 		log.Printf("latest poll %s: eligible count: %v", name, err)
+		st.Gap = defaultGap
 		return defaultGap
 	}
 	gap, clamped := effectiveGap(s, eligible)
+	st.Gap, st.Clamped = gap, clamped
 	if clamped {
 		log.Printf("latest poll %s: gap clamped to %s floor (eligible series=%d)", name, minGap, eligible)
 	}
@@ -278,7 +293,6 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 	}
 
 	refusals := 0
-	checked := 0
 	for i, sr := range due {
 		if ctx.Err() != nil {
 			break
@@ -313,10 +327,10 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 		} else {
 			refusals = 0
 		}
-		checked++
+		st.Checked++
 	}
-	if checked > 0 {
-		log.Printf("latest poll %s: due=%d checked=%d", name, len(due), checked)
+	if st.Checked > 0 {
+		log.Printf("latest poll %s: due=%d checked=%d", name, len(due), st.Checked)
 	}
 	if refusals >= 2 {
 		p.setRefusalBackoff(name, now.Add(refuseBackoff))