Refresh cead's assets: Irish accents, feathered Ogham mark, SVG lockups

[1zeroone0]

What this PR does

A fresh asset set that matches cead's Irish name and Ogham mark.

• Accents: a deep forest green and a burnt orange, the tricolour's hues kept muted and matte.

  Role	Before	After	OKLCH (L, C, h)
  lichen (permit)	#5f7a45	#2f5f43	0.45, 0.07, 155
  iron (forbid)	#b3402f	#a95a27	0.55, 0.12, 50

• The mark: Ogham c, e, a, d on its original grid (20 px strokes, 44 px pitch), the stem trimmed to the lettering and closed with feather marks (᚛ ᚜) as in manuscript Ogham; the green a stroke runs unbroken across the stem. Groups keep Ogham's even rhythm rather than sitting over their Latin letters.

• Lockups are SVG and are their own source: the mark is rects and lines, the letters are traced from the previous raster.

  • lockup.svg, lockup-light.svg: the README's stacked lockup for dark and light themes, switched with <picture>. Before, the stone letters vanished on GitHub's light theme.
  • lockup-source.svg: stacked, stone on slate, no accents, for places that cannot render color (a terminal).
  • lockup-source-color.svg: the same with accents.

• palette.png, terminal-mockup.png regenerated in Fira Code with current vocabulary: verdicts permit/forbid (CODE.md), the shell prompt [step 12/100] (Loop: one machine, one process, done #8), "process" for "node"; the header mark is stone-only.

• Caption: the name's gloss becomes a centered caption under the lockup instead of a dangler after the opening paragraph.

What this PR does not do

• Commit a generator. The SVGs are hand-editable sources; the two PNGs are mockups, regenerated by a one-off script.
• Match the old monospace face exactly (it was JetBrains Mono or similar, not installed); Fira Code is used throughout.
• Rename the swatches (lichen, iron).

Merge requirements

• Operator approves the README top on GitHub in light and dark mode. Known tradeoff: forest green on dark grounds is 2.5:1 contrast (the permit word in the mockup).
• Every asset uses the new accents; no PNG lockup remains.

🤖 Generated with Claude Code

[1zeroone0]

1. Built — accents recolored in three PNGs: pixel blend-solve against the ground, then re-blend with the new accent; hex labels spliced from existing glyphs.
2. Why — flag hues, muted chroma, deeper per review. Rejected: a generator script (maintenance with no source to generate from); re-rendering labels with a guessed font.
3. Bloat — lockup's second iron merged into one.
4. Drift — palette.png is the only place hex values live; updated.
5. Trust surface — checked by pixel diff (changes confined to accent regions, no old accent left) and by eye at zoom. No automated check.
6. How it breaks — GitHub dark mode: green on dark ground is low contrast (2.5:1). Future edits need the same one-off approach until there's a vector source.
7. Not confident — merging the lockup's darker iron; green lightness on dark grounds.
8. Verify yourself — README lockup in GitHub dark mode; cead green in terminal-mockup.png.
9. Next steps — finished pending hue approval.

[1zeroone0]

1. Built — in lockup.png, the stem rows under the green a stroke are painted with the stroke's own column, composited over the stem so the edges keep their antialiasing.
2. Why — the accent stroke should read as one continuous mark; white e strokes merge with the white stem, so only the green one needed it.
3. Bloat — none added; one file changed.
4. Drift — PR description updated.
5. Trust surface — checked by eye at 4× zoom on a dark ground. Only rows 170–189, columns 588–611 changed.
6. How it breaks — the orange d strokes sit above the stem and touch it; they were not changed. If you want those in front too, same fix.
7. Not confident — nothing specific.
8. Verify yourself — the lockup on the README in GitHub dark mode.
9. Next steps — finished; ready for review.

[1zeroone0]

1. Built — the Ogham row of lockup.png redrawn from measured geometry: stem trimmed and centered, feather marks drawn supersampled and composited over; lockup-light.png is the same drawing with stone mapped to ink; README switches between them with <picture>.
2. Why — option A (keep Ogham's rhythm) over aligning groups to Latin letters, which would break the script's even spacing. Feathers: historically accurate for the manuscript line, and they read like a cursor.
3. Bloat — one new asset, required for light mode; no scripts committed.
4. Drift — PR description rewritten to the current scope; lockup-source and the mockup's small mark noted as not updated.
5. Trust surface — checked by eye on GitHub's dark (#0d1117) and white grounds; zero stone pixels remain in the light variant. <picture> rendering on GitHub not yet seen.
6. How it breaks — GitHub mobile or other renderers that ignore <source media> fall back to the dark variant, which is invisible on white.
7. Not confident — feather size and angle; stem length (feather tips extend 20 px past the lettering).
8. Verify yourself — the PR's README preview in both GitHub themes.
9. Next steps — finished; ready for review.

[1zeroone0]

1. Built — four SVG lockups (mark from its grid, letters traced with potrace at 4× from the old raster); palette and terminal mockup regenerated in Fira Code.
2. Why — SVG makes the lockup its own source, which ends the raster patching; PNG stays for the two text mockups.
3. Bloat — three PNG lockups deleted; four SVGs added, each a distinct use (dark, light, mono source, color source).
4. Drift — mockup vocabulary aligned with CODE.md and Loop: one machine, one process, done #8; README points at the SVGs.
5. Trust surface — each SVG rasterized with resvg and checked by eye on GitHub's dark and white grounds. Not seen on GitHub itself.
6. How it breaks — traced letters are a close approximation, not the original font; a renderer ignoring <source media> shows the dark lockup on white.
7. Not confident — palette descriptions' wording; whether the stone-only header mark in the mockup is what you meant for terminals.
8. Verify yourself — the README preview in both themes; terminal-mockup.png.
9. Next steps — finished; ready for review.