Rendered instrument UI and the shared Affine design language

[user1303836]

Rebuilds the Suppressor editor as rendered matte black hardware and introduces the Affine design language, a shared kit that HDN Ring Modulator adopts in affinedsp/hdn-ringmod#38 (companion PR).

Real capture from the UI tests: six seconds of plucked notes processed at real-time pace, suppressing between notes.

This design was chosen from four alternatives (#4, #5 and #6, plus the original design first proposed here). The chosen one, Stealth (#6), is merged into this branch, and the shared kit is reduced to it.

What changed

• libs/affine-ui (new, identical in both repos): the affine_ui JUCE module (v3.0), bundled OFL fonts, and DESIGN_LANGUAGE.md. The powder-coat panel and the knobs are shaded per pixel at the display's physical scale and cached, so they stay sharp from 100% to 200% and on Retina. Only moving parts repaint. A product sets only its screen colour.
• Editor, 640×460 → 820×540: a black powder-coated panel with colour only on one teal screen.
  • Screen: high-band reduction over the last six seconds, with the current value above the plot. The plot breaks wherever there was no reading. Beside it are INPUT and OUTPUT peak bars with readouts and clip cells; OUTPUT is relabelled REMOVED while auditioning.
  • Controls: Threshold, Strength and Release are knobs inside white LED rings, with printed scales and glass readouts. Listen removed is a soft key with a headphones glyph and an amber LED strip.
  • Status: the processing state with its LED (teal suppressing, amber listening or learning, red bypassed, off without audio), and Host settings active when legacy settings differ from their defaults.
• Removed: PluginLookAndFeel.* and assets/fonts (the fonts now live in the shared kit).
• Docs: docs/UI_DESIGN.md is rewritten for this editor (the previous version still described an older 1000×640 layout with 20 controls), and the README and state screenshots are refreshed from the UI test captures.

Preserved behaviour

• DSP, processor, parameter IDs, ranges, defaults, text conversion, state and automation are untouched.
• Metering semantics are unchanged. Readings only count as live from a new block within 500 ms whose routing matches. Stale data goes dark: the status LED goes out, the bars go dark, readouts show -- and the plot breaks. Multiband mode still disables Threshold and Strength. The status strings and the accessible meter summary are the same.
• Knob interaction is the same contract as before: 240 px drag, Shift for fine, strict exact entry, Alt/Option-click or Home to reset, arrows, and the host context menu. Every edit is one gesture.

Listening to the removed signal	Learning bands (multiband)

Verification (macOS, arm64)

• ctest: 2/2 pass. The UI suite has 8 cases and 435 assertions. It covers bundled fonts and contrast (including the screen colour), the native VST3 and CLAP editor embedding and lifecycle, exact entry, gestures, state recall, truthful live, stale, bypass, audition and learning states, clip reporting, and rendering at 100–200%.
• pluginval 1.0.4 at strictness 10 reports SUCCESS for the VST3.
• CI builds and captures every state on Windows and Linux; captures are in the ui-evidence-* artifacts.

Notes for review

• The design language and shared kit are vendored, not submoduled, so each repo stays self-contained. If you'd rather keep them in their own affinedsp/affine-ui repo, moving the folder there is mechanical.
• The branch history includes the alternatives round: kit 2.0 added four finishes and the last kit commit removes the three that were not chosen. The final diff contains only the Stealth kit.
• The maker's mark reads "affine" to match the org. The plugin's company name and codes are unchanged.