feat(polish): close all 6 review nitpicks in one sweep

closes board-viewer-polish

- M1 src/parser.ts: comment explaining why **Status:** text field is intentionally
  ignored (emoji is canonical, prevents future-reader head-scratch)
- M2 src/render.ts + tests: clamp future ISO to '0m' (server clock drift safety)
  + inline comment + test
- M3 .tasks/board-viewer-gitea-reader.md: decisions-log clarifying orphan
  per-task files are out of scope by design (STATUS.md = index of record)
- M4 static/board.{js,css} + src/render.ts: filter rebuilt to query records
  (not DOM badge text); 5 status-filter pill buttons in header with active
  toggle state; smoke-verified blocked filter
- M5 deploy/Dockerfile.build: HEALTHCHECK (file fresher than 2×tick) and
  stderr redirect for failures with timestamp
- M6 src/reader.ts: parallelize getLatestCommitIso per-repo via Promise.all
  (preserves block order)

49 tests pass (was 43 pre-polish), typecheck clean, smoke against real Gitea
returns 81 records from 4 repos.

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

static/board.css

@@ -81,6 +81,36 @@ header h1 {
   font-variant-numeric: tabular-nums;
 }
 
+.status-filters {
+  display: flex;
+  gap: 0.4rem;
+  flex-wrap: wrap;
+  margin-top: 0.5rem;
+  width: 100%;
+}
+
+.status-filter {
+  font: inherit;
+  font-size: 0.75rem;
+  padding: 0.2rem 0.55rem;
+  background: transparent;
+  border: 1px solid var(--border);
+  border-radius: 999px;
+  color: var(--muted);
+  cursor: pointer;
+  transition: border-color 0.12s, background 0.12s, color 0.12s;
+}
+
+.status-filter:hover {
+  border-color: var(--muted);
+}
+
+.status-filter.active {
+  background: var(--accent);
+  color: var(--bg);
+  border-color: var(--accent);
+}
+
 main.board {
   display: grid;
   grid-template-columns: repeat(5, minmax(14rem, 1fr));