style: refine sprint gallery cells

[numnx]

What changed

• Simplified sprint gallery cells around the unified interactive workflow badge by removing duplicate hover lifecycle and standalone merge-conflict badges.
• Reworked sprint keys into an unboxed blue ID lockup and removed the nested metrics card around task/completion counts.
• Limited the external Waiting for you cue to genuinely human-owned open intervention, positioned it 10px above the cell, and reserved the red perimeter for execution failures.
• Replaced the rejected liquid simulation with a lightweight, Material-inspired SVG wave composition for active cells. Three softly blurred blue/cyan/violet layers move slowly with GSAP and become fully static under reduced motion.
• Increased gallery row spacing for the external attention cue and updated canonical/public dashboard documentation.

Why

The gallery had competing status signals and overly heavy active-state motion. This change gives workflow state one clear authority, separates human attention from worker-actionable work, and gives active cells a quieter, more polished visual identity without sacrificing accessibility or bundle efficiency.

User impact

• Sprint state and action ownership are easier to scan.
• Worker-owned merge conflicts no longer look like requests for manual intervention.
• Active cells remain visually distinctive without continuous glossy or high-amplitude animation.
• Keyboard, semantic-status, and reduced-motion behavior are preserved.

Validation

• pnpm run lint — passed
• Focused sprint visual/status tests — 31 passed
• pnpm run test:dashboard — 252 files passed; 2,278 passed, 1 skipped
• pnpm run build — passed
• Local browser visual inspection at 1600×1200 — passed
• pnpm run test:backend — 449/450 files passed; the containerized local-merge case failed only in the concurrent full suite, while its isolated rerun passed all 40 tests

Risk and rollback

Risk is limited to sprint-gallery presentation and status-cue visibility. Reverting commit c98efdcbe restores the previous gallery treatment.