fix(card): eliminate frame overflows and add release-gate standard (#8)

Three cards overflowed the 340×200 frame for realistic profile data:

- contributions-heatmap: the classic case — 53 weeks at 9px cellSize + 2px
  gap pushed the grid out to x≈611. Shrink to cellSize=5, cellGap=1 so
  leftPad(22) + 53*6 = 340 (exact fit). Drop month labels within 20 px of
  the right edge so "Dec"/"Apr" can't stick past the frame.
- streak: the third column rendered "N / M" at font-size 28, centered at
  x=282. For 4+ digit totals (e.g. 584 / 3031) the text extended to x≈347.
  Refactor to show the active-days integer by itself in the big slot and
  push "of N total (P%)" into the small detail line that the other two
  columns already use.
- top-starred-repos: the per-row star icon sat at x=306 while the right-
  anchored number ended at x=334, so 5+ digit star counts collided with
  the icon. Drop the icon (card title already says "Top Starred Repos"),
  emit the count as "N ★", right-anchor at x=334 with a 6 px safety gap.

Add a new TestCardsFitFrame stress test that renders every card against an
adversarial profile (10-digit counts, 40-char names, 20 active years,
53-week span) and asserts every positional attribute stays inside the
frame. This is the automated half of the new "fit-the-frame invariant"
added to docs/design-guidelines.md + a pre-release review checklist in
docs/code-standards.md.

Bug reports will still surface text-overflow cases that the coordinate
check can't see (a text-anchor="middle" element has a single x attribute
but renders outward), so the docs also spell out the human-review step:
render dracula against tiny/typical/adversarial fixtures before release.

docs/code-standards.md

@@ -84,6 +84,17 @@ go build ./...
 
 All three must pass. If a test is failing, fix the test before committing — don't skip.
 
+## Card review checklist (pre-release)
+
+In addition to the compile/test gate above, any change that touches files under `internal/card/` **must** be reviewed against `docs/design-guidelines.md` → "Fit-the-frame invariant" before merging. Specifically:
+
+- Render the dracula theme against the **tiny / typical / adversarial** profile fixtures and visually verify nothing overflows or overlaps.
+- No hard-coded dimensions that only work for the reviewer's own profile (names, digit counts, year spans).
+- Every right-anchored value or text-anchor="middle" element fits inside its column / safety margin.
+- The CI-built `demo/<theme>/` gallery is the canonical "dracula on the author's profile" view; don't rely on a local run alone.
+
+This is a hard gate: a card that overflows on a realistic profile does not ship, even if tests pass.
+
 ## Dependency policy
 
 - **Stdlib only.** `go.mod` lists no `require` entries.