fix(ui): walk the eleven dangling-style reports — two were real

#2444. Each needed reading rather than a batch fix, and the split was 2 real
losses, 4 false reports, 5 wrappers that are bare on purpose.

REAL:

  .system-card   was a flex row, and every child still says so —
                 .system-swatch and .system-actions are flex-shrink: 0,
                 .system-body and .system-form--inline are flex: 1.
                 align-items: flex-start is why the swatch carries
                 margin-top: 0.3rem: nudged onto the first line of text.
  .systems-list  no rule AT ALL, so the systems list rendered with browser
                 bullets and indent. Invisible to the check — see below.
  .graph-embed   the panel is a flex column whose header is flex-shrink: 0,
                 so this is the item that takes the remaining height. Without
                 it the `height: 100%` on the line below resolves against auto
                 and does nothing, which left the comment above it specifying
                 a rule that could not work.

FALSE REPORTS, and the checker was wrong rather than the code:

`.pane.empty` and `td.num` are base rules for the element that carries those
classes — the check read any compound with more than a lone class as a
modifier. It now records a compound's whole class SET and clears an element
carrying all of them, which is exact: recording the classes individually would
have cleared `.pane` everywhere on the strength of a rule that only applies
alongside `.empty`. Four reports gone, and a check with false reports is one
that gets skimmed.

BARE ON PURPOSE — .rb, .topic-group, .new-topic, .sub-list, .dash-head, and
both .detail-row rows. Each namespaces descendant rules and assumes nothing
about layout, which is the tell that separates them from a deleted base. All
seven now carry a comment saying so, so the next reader doesn't re-litigate
them and a NEW entry in the report means something actually changed.

Also recorded in the script: it cannot see a class with no rule anywhere, since
that is indistinguishable from a semantic-only hook. `.systems-list` was found
by reading the file beside a class that WAS half-styled.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

frontend/src/components/rules/RulebookDetailPane.vue

@@ -135,6 +135,11 @@ ul { list-style: none; padding: 0; margin: 1rem 0; }
 li { padding: 0.5rem; cursor: pointer; border-radius: 6px; }
 li.active { background: var(--color-primary-bg); }
 li:hover { background: var(--color-hover); }
+/* `.new-topic` and `.sub-list` are deliberately bare (#2444). The first wraps a
+   button-or-form whose children style themselves; the second is a `<ul>`, and
+   the bare `ul` rule above already gives it list-style, padding and margin —
+   a base a class-name check cannot see, since it comes from an element
+   selector. Both namespace descendant rules and assume nothing about layout. */
 .new-topic input {
   width: 100%; margin-bottom: 0.5rem;
   background: var(--color-bg); color: inherit;