chore: record the control panel's design history and visual reference

[REPPL]

This PR changes records only; no code changes. It is stacked on #205: both add a line to the end of .abcd/work/DECISIONS.md. Once #205 merges, this PR moves onto main.

The maintainer judged all ten control-panel designs from two rounds in one assessment. They chose design 8 ("Tahoe glass") as the base, then changed parts of it and borrowed parts of designs 9 and 7.

What's added

• .abcd/work/design/2026-10-10-control-panel/, the design history:
  • both briefs, with machine paths replaced by repository paths;
  • the ten designs, each a self-contained HTML page that opens from disk;
  • the full assessment result (JSON);
  • a README holding the criteria, both rounds, the ranking and the decision. The maintainer's verdicts are quoted verbatim, and its known gaps and next steps are listed.
• .abcd/development/design/taste.md: lasting lessons on what to keep and what to avoid, each linked to the design history it comes from. It describes past judgements and does not override a new brief.
• itd-2609100519003748: a new Design Reference section, placed before Audit Notes and away from chore: record the dashboard lab's rulings and two issues #205's edits. The intent still passes abcd intent ready.
• .abcd/work/DECISIONS.md: one dated line.

The decision in short

Changes to 8:

• The sidebar can be hidden.
• The top navigation uses icons instead of group labels.
• Buttons feel native.
• Cards expand smoothly.
• The save bar is set apart from the cards.
• Cards use the width of large screens.

Borrowed: design 9's detail sheet on the right, its button placement and its bar chart; design 7's "More" pop-out.

Assessment, briefly

• 30 side-by-side pairs, 5 of them repeats; the maintainer answered all 5 repeats the same way.
• All five round-2 designs ranked above all five round-1 designs.
• The pairs did not separate the top four; the criteria scoring brought out the differences. The README sets out these limits.

Still owed

• The panel spec (spc-2609201007368529) is re-planned to carry the Overview and this reference.
• The status shapes the agents chose (ready, working, failed) have not been put to the maintainer.

Checks

• abcd intent ready itd-2609100519003748: ready
• abcd lint: 168 findings, the same as the base branch
• go test ./internal/archtest/: ok
• gitleaks over the new design folder: no leaks