feat: right-edge trace controls, one tooltip grammar, a version tip that pitches

[lroolle]

UI polish pass + release prep for 0.31.0.

• Session view trace controls (replay, ⌘ actions) right-align to the page edge — the requests view's filter input already held them there, so the controls now keep one position in both views instead of hugging the tabs when the filter is hidden (margin-left:auto on #replay-toggle).
• Every toolbar/header/replay-bar tooltip restructured into the designed tip grammar (heading line, --- divider, "> " interaction hints) instead of one-line em-dash run-ons: replay documents its whole key map, purge says "no undo" up front, select names its Esc exit, mask/theme/instances/version all match the data surfaces' hover language.
• Version badge hover rebuilt as a miniature release note: one-line slogan, the traced clients, and a fresh-features list (refresh at release — noted in renderVer and the release flow).
• CHANGELOG 0.31.0 (covers feat: trace identity in the traced child's env (proxy modes) #75's trace-identity env too), version bump, CLAUDE.md + skills/cctrace/SKILL.md sync.

Verified in Chrome against a real 546-pair trace: both views, replay tooltip, version tip. 564 tests green.

🤖 Generated with Claude Code