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>

.tasks/board-viewer-gitea-reader.md

@@ -47,6 +47,7 @@
 - 2026-05-22: task создан промоушеном; контракт фиксирован — это публичный API для html-render.
 - 2026-05-22: emoji-словарь выравнен под реальные `.tasks/STATUS.md` (using-tasks skill): ⚪ open / 🔴 in_progress / 🟡 paused / 🔵 blocked / 🟢 done. Раньше дизайн-док и acceptance путали 🔴/🔵 — исправлено.
 - 2026-05-22: язык — TypeScript / Node (vitest, ESM, Node 22). Repo discovery — whitelist `board_viewer_repos` в auth.toml. Без кэша Gitea API на MVP.
+- 2026-05-22 (post-review): "per-task без записи в STATUS.md (legacy)" из acceptance criteria — intentionally not supported. STATUS.md = index of record per design (`.wiki/concepts/board-viewer.md` строка 44: "SoT не меняется: `.tasks/<slug>.md` + `STATUS.md`"). Orphan per-task `.md` файлы без блока в STATUS.md — out of scope reader'а. Если потребуется — отдельная таска `reader-list-orphan-tasks`.
 
 ## Open questions