web: site-completed hint reaches the owner, decides nothing (#170)

The Site's own completed marker (issue #168) joins the owner's surface as
an informational hint, never a decision:

- store: SeriesFilterSiteCompleted ('site_completed') sits beside Finished
  in the filter vocabulary; its predicate carries the same finished_at
  guard as the clock-driven filters, because the Site's stamp keeps
  standing after the owner retires the row. The projection and SeriesPage
  GROUP BY carry site_completed_at so the detail page can age it.
- web: the filter joins the Series list select as 'Site says completed'
  and rides the tail of seriesFilterOrder, so the landing stats figure
  comes for free and sits after the finished figure.
- detail: one hint line beside the Finish control - 'the site says this
  work is completed (since 3d ago)' - rendered only while the stamp
  stands and no Finish stands; the Finish control itself is untouched.
- tests: filter's finished exclusion and un-finish return to the Poll
  query (store); figure at zero and nonzero, hint present/absent, and the
  Finish control's markup byte-identical with a hint present (web).

backend/internal/web/admin_overview.go

@@ -23,10 +23,10 @@ type overviewView struct {
 	// as stale + never_checked: a never-checked Series is already counted on
 	// its own filter, and the verdict wants the inclusive number.
 	Unchecked int
-	// Hygiene is the seven problem filters in the Series list's own render
-	// order plus the finished figure riding last (informational); Library is
-	// the library split plus the roster. Every figure is a door into the list
-	// that counts it, except a zero.
+	// Hygiene is the problem filters in the Series list's own render order
+	// plus the informational tail — finished, then site completed — riding
+	// last; Library is the library split plus the roster. Every figure is a
+	// door into the list that counts it, except a zero.
 	Hygiene []fig
 	Library []fig
 	// Sites is the per-Site library shape table, one row per Site with any
@@ -60,7 +60,7 @@ type siteRow struct {
 }
 
 // overviewView assembles the landing page from the store's read model: one
-// SeriesShapes pass per filter summed in Go (the shipped surface offers nine
+// SeriesShapes pass per filter summed in Go (the shipped surface offers ten
 // grouped passes, not a stats query — #140), the pass log's latest pass per
 // Site, and the roster. A failure in any read is a 500 with a logged reason,
 // never a page of silent zeroes.
@@ -94,10 +94,10 @@ func (h *Handler) overviewView() (overviewView, error) {
 	view.Unchecked = totals[store.SeriesFilterStale] + totals[store.SeriesFilterNeverChecked]
 	view.Verdict, view.HasCounts = overviewVerdict(passes, now)
 
-	// The hygiene figures, in seriesFilterOrder's tail: the seven problem
-	// filters in permanent-then-fixable order, then the finished figure last —
-	// informational, not a problem, and last because seriesFilterOrder appends
-	// it there. The All filter's count belongs to the Library block, not to a
+	// The hygiene figures, in seriesFilterOrder's tail: the problem filters
+	// in permanent-then-fixable order, then the informational tail — finished
+	// and site completed — riding last because seriesFilterOrder appends them
+	// there. The All filter's count belongs to the Library block, not to a
 	// "hygiene" figure.
 	hygiene := make([]fig, 0, len(seriesFilterOrder)-1)
 	for _, name := range seriesFilterOrder[1:] {