feat(ui): CoachTip coaching tooltip component (RIG-2703)

[rigel-mintaka]

This PR is part of a stack containing 4 PRs:

1. main
2. feat(keyboard): sequence-grammar chord helpers for leader chords (RIG-2707) #612
3. "feat(ui): CoachTip coaching tooltip component (RIG-2703)" (this PR)
4. feat(ui): adopt CoachTip across command-backed chrome + register sidebar toggles (RIG-2704) #618
5. docs(ui): document the shipped CoachTip consumer + retarget the ShortcutChip note (RIG-2705) #620

Adds the reusable coaching Tooltip from the frozen coaching-tooltips design (docs/designs/product/compass-coaching-tooltips/design.md, T1 / §A1-A3, A5, D5): a label + keymap-resolved chord that reveals on hover AND focus, in the shipped .cx-tooltip box. This is the component only; the adoption sweep across command-backed chrome is T2 (RIG-2704).

• apps/ui/src/components/CoachTip.tsx — three exports mirroring Kobalte's own anatomy: COACH_TIP_DELAY_MS = 400 (mirrors the --cx-tooltip-delay token, tokens.css:227); CoachTip, the Kobalte v2-alpha Tooltip root with openDelay defaulted to that constant and hover+focus reveal (Kobalte's default, triggerOnFocusOnly unset); CoachTipTrigger, the re-exported polymorphic Tooltip.Trigger so call sites author their own element; and CoachTipContent, the Tooltip.Portal + Tooltip.Content(class="cx-tooltip") rendering the label and, right of it, the chord.
• Chord is always the keymap-resolved display string — props.chord ?? shortcutFor(props.command, detectPlatform()), never hand-authored (DL-234's single-derivation rule). undefined → label-only; a " then " leader sequence → plain text in the chip's typographic style; any other chord → <ShortcutChip>. Because the component only reads shortcutFor's output, it shows Ctrl+B/Cmd+B today and G then B automatically once the leader-chord rows land — no merge-order dependency. Props are never destructured (Solid v2 reactivity).
• apps/ui/src/design/components/tooltip.css — the box (.cx-tooltip, whose first consumer this is) becomes a flex row and gains a .cx-tooltip-label sub-part, so the label takes free space and the reused .cx-palette-shortcut chord chip right-aligns via its own margin-left: auto.

Tests (CoachTip.test.tsx, @solidjs/testing-library): label + chord derived from shortcutFor (never a hand-authored expectation); the ARIA wiring Kobalte owns (role="tooltip" + aria-describedby); focus reveal with no pointer event; the label-only path for a command with no keymap row; and the sequence-aware branch, whose "G then B" fixture is derived from formatChordForDisplay("G B", "other") so a change to the shared format contract surfaces here as a failing test rather than a giant <kbd>.

Stacked on RIG-2707 (the formatChordForDisplay sequence-grammar root the sequence branch keys off).

Ledger-impact: none. DL-245..247 for this record landed with the design PR (#569); this impl slice ratifies no new decision.

Refs RIG-2703

Co-authored-by: Matt Wilkinson matt@rigel.build

[linear-code]

RIG-2703

[github-actions]

Compass engineering docs preview: https://compass-ux-rig-2703-coachtip.compass-eng-docs.pages.dev

Deployed from compass-ux/rig-2703-coachtip-component at f28db7f.