Diffs name their chain; history shows the ruleset's diff

The ruleset's diff names the chain each hunk is in on its @@ line, as
git names the function. A history entry shows what it did to the
ruleset (web page, hc history diff, GET /history/{id}/diff), rebuilt
from the current configuration by stepping back through the later
entries. A changed setting is listed by its own fields
(builtins.drop_invalid) instead of the whole object.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/assets/style.css

@@ -409,6 +409,7 @@ input.wide { width: 100%; }
 .diff .add { background: var(--add); color: var(--add-text); }
 .diff .del { background: var(--del); color: var(--del-text); }
 .diff .hunk { background: var(--hunk); color: var(--accent); }
+.diff .hunk .block { font-weight: 700; color: var(--text); }
 .diff .file { font-weight: 700; padding-top: 6px; }
 select.inline { width: auto; display: inline-block; }
 /* The rule dialog's optional parts: "+" buttons, and ✕ to close one. */