[rebrand] Modernize puzzle-complete feedback dialog paint

[alex-m-brown]

Repaints the shared puzzle-complete feedback dialog (opened by FeedbackUtils.displayFeedback after Run in any Blockly/Droplet lab) with semantic design-system tokens. No LegacyDialog shell swap - CSS-only paint plus small source-level color swaps in LegacyButton.jsx

Scope: puzzle-complete dialog specifically. Everything else scoped under .dash_modal so it doesn't touch react-bootstrap modals in PD/account/teacher-tools surfaces.

What changed

• Close X: dropped the giant 61x59 PNG close-button mixin; renders a small fa-solid fa-xmark in --text-neutral-quaternary, transparent bg. Same treatment as the qtip PR. One line in LegacyDialog.js adds <i class="fa-solid fa-xmark"> inside the button.
• Title / body typography: .congrats and .lines-of-code-message swap legacy $neutral_dark + main-font-semi-bold for --font-family-main + --font-size-body-lg + --font-weight-semi-bold/-regular + --text-neutral-primary. Targets specific classes so the Show Code panel's own p/pre inside .generated-code-container is untouched.
• Show Code toggle: .show-code > summary gets semantic tokens + DS type. !important needed because CodeWritten writes inline styles on the summary.
• Buttons row: #feedbackButtons is a right-aligned flex row (24px gap, align-items: center so K1 Replay sits centered against the tall Continue arrow). The button colors themselves are set at source in LegacyButton.jsx (see below), so no !important color overrides in the SCSS.
• BUTTON_TYPES.legacyPrimary (LegacyButton.jsx): color.orange -> var(--background-brand-purple-primary) for bg + border. Radium's inline style passes the CSS var through; the browser resolves it. This is the only reason the K1 Continue arrow head recolors automatically - the head reads config.style.backgroundColor at render time. Blast radius: legacyPrimary is only used by DialogButtons for the Continue button, and Continue only renders when the caller passes nextLevel={true} - which is only displayFeedback in puzzle-complete. No other button in the app changes color.
• BUTTON_TYPES.cancel (LegacyButton.jsx): neutral_white / neutral_dark / neutral_dark20 -> --background-neutral-primary / --borders-neutral-strong / --text-neutral-primary / --background-neutral-tertiary (hover). Blast radius: ~15 dialog Cancel/Replay buttons across weblab/javalab/applab/levelbuilder/data-browser plus feedback's Replay. Visual delta is subtle in light theme (#292F36 -> #9ea5ad border tint); semantically correct.
• Puzzle rating row: kept in the DOM (downstream tests depend on it) and rebranded to match - --borders-neutral-primary separator, Geist 16px --text-neutral-tertiary label, heart/frown icons in --text-neutral-quaternary at rest / --text-neutral-primary when hovered or enabled.

Testing story

Before screenshots

After screenshot

Then manually test:

• Complete a puzzle in any Blockly/Droplet lab (Artist, Maze, Play Lab, App Lab, Sprite Lab) and confirm the dialog renders with modern typography, purple Continue, outlined Replay, small fa-xmark close, and rebranded puzzle rating row.
• Complete a K1 puzzle (Course A or B kindergarten level) and confirm Continue is a purple arrow (body + head both purple), Replay is the K1 chunky outlined variant vertically centered against the arrow, and the puzzle rating row still renders.
• Click the heart / frown - confirm the enabled state darkens correctly and only one is selected at a time.

• Expand "Show code" and confirm the code panel inside is unchanged (dark text on neutral gray, monospace, Berkeley/Harvard links still work).
• Close the dialog via the X, via Escape (Bootstrap modal default), and via Continue / Replay.
• Trigger a Cancel button elsewhere in the app (any weblab/javalab/applab/levelbuilder/data-browser dialog with a Cancel) and confirm the subtle border-color shift looks OK (was near-black, now medium-gray).
• Sanity-check a non-lab surface (a PD dialog, an account settings modal) to confirm the rebranded typography does NOT leak in (everything CSS-side is scoped to .dash_modal).
• Try RTL (html[dir=rtl]): X should flip to left, layout should mirror, K1 arrow should still point in the correct direction.
• Firefox and Safari.

Make sure you ask @:

• Continue uses --background-brand-purple-primary; Replay is --background-neutral-primary with --borders-neutral-strong border. Confirm this is the right pairing for the puzzle-complete surface.
• Cancel button retokenization softens the near-black border to a medium-gray across ~15 dialogs (list in "What changed" above). Confirm this is acceptable collateral rebrand or if you'd prefer we keep those legacy and only paint feedback's Replay.