fix(card): show 7 *named* languages + Other, not 6 + Other (#19)

With topN=7 the previous collapseOther kept only the first 6 entries
and added "Other" as the 7th row. A user expecting to see 7 actual
languages in the legend saw six named languages plus "Other" — the
exact complaint just raised about the profile repo's donut.

Flip the semantic: the "top N" slots are reserved for real languages,
and "Other" is an extra row when (and only when) there's a non-zero
tail past the Nth entry. Topologically that means up to 8 legend
rows — still fits the card frame (row 8 text baseline at y=195, card
height 200).

- TestDonutTopSevenPlusOther pins the new contract with a 9-language
  input.
- adversarialProfile in TestCardsFitFrame bumped to 9 languages so
  the stress test exercises the 8-row legend geometry.
- design-guidelines: the donut row re-reads "Up to 7 named languages,
  plus an 'Other' row when the tail is non-zero (8 rows max)".

docs/design-guidelines.md

@@ -50,7 +50,7 @@ Cap rows at what fits: up to 7 rows per card. Stats splits commits into lifetime
 | Donut centre | `(250, 110)` |
 | Outer radius | 55 |
 | Inner radius | 30 |
-| Top-N entries shown | 7 (overflow collapses into "Other") |
+| Top-N entries shown | Up to 7 named languages, plus an "Other" row when the tail is non-zero (8 rows max) |
 | Slice stroke | `theme.Background`, 1.5 px (gap between slices) |
 | Legend origin | `(20, 55)` |
 | Legend row height | 20 px |