feat(harness): declare intentional N/A tiers + custom-html-tiny functional test

Two changes the operator asked for after noticing custom-html-tiny PR #6 has no
backup/restore or functional coverage:

1) Intentional-vs-accidental N/A. A recipe can now declare
   recipe_meta.EXPECTED_NA = {rung: reason} to mark a tier as deliberately not
   applicable (e.g. a stateless static server has no backup surface). N/A still
   caps the level — the harness never claims a rung it did not verify — but the
   run is now annotated 'intentional · <reason>' instead of being indistinguishable
   from a forgotten test. An *undeclared* N/A on a gap-sensitive rung
   (backup_restore, functional) is surfaced as a 'possible coverage gap', and a
   stale EXPECTED_NA (declared N/A but actually exercised) is surfaced too. All
   non-blocking (R7): results.json gains level_cap_intent + an  block, the
   summary card shows the clause, and the CI log prints the gap/stale warnings.
   (results.classify_na/cap_intent are pure + unit-tested; level.py untouched.)

   custom-html-tiny declares backup_restore intentionally N/A.

2) custom-html-tiny functional test: writes a random file into the served content
   volume (via the volume mountpoint, like install_steps.sh, since the SWS image
   is shell-less), asserts exact-byte round-trip + a real 404 on a missing path —
   proving the static-web-server actually serves the volume, not a 200-everything
   fallback.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

runner/harness/card.py

@@ -116,7 +116,9 @@ def render_card_html(data: dict, screenshot_rel: str | None = "screenshot.png")
     recipe = html.escape(str(data.get("recipe", "?")))
     version = html.escape(str(data.get("version") or data.get("ref") or ""))
     level = int(data.get("level", 0))
-    cap = html.escape(str(data.get("level_cap_reason") or ""))
+    cap_reason = str(data.get("level_cap_reason") or "")
+    cap_intent = str(data.get("level_cap_intent") or "")
+    cap = html.escape(cap_reason + (f" · {cap_intent}" if cap_intent else ""))
     color = level_color(level)
     flags = data.get("flags", {}) or {}
     flag_bits = []