fix(design): purge the last purple from /docs and de-darken /admin/spine #5459

Part of the visual-audit ledger sweep — refs #211. Slice: DOCS + ADMIN SPINE BOARD.

/docs — the site's one explicit no-purple violation (src/routes/docs.tsx)

• Sidebar active pill — .docs-nav-active set color: #c4b6ff (light purple). Now var(--accent) over the existing color-mix(in srgb, var(--accent) 14%, transparent) background: evergreen pill, subtle accent wash.
• Inline code — .docs-content code used the same #c4b6ff purple → var(--accent).
• Code blocks — .docs-content pre hardcoded a dark panel (background: #0a0c14, color: #d6d8e3) onto the warm-paper page → var(--bg-tertiary) / var(--text), so it renders paper-toned in light and slate in dark. No other purple/indigo literals remain in the file.

/admin/spine — dark panels + invisible name column (src/routes/admin-spine.tsx)

Root cause: spineStyles referenced tokens that do not exist in design-tokens.ts — var(--bg-subtle, #161b22) and var(--border-muted, #21262d) — so the GitHub-dark hex fallbacks always won. Every hero/section panel rendered #161b22 inside the light theme, and .spine-name (no color of its own) inherited the light theme's dark ink onto that dark panel — the 14 check rows showing only "Green · 5m ago".

• All panels/borders/text now read real tokens defined in both theme blocks: --bg-elevated, --border, --border-subtle, --text-muted, --text-strong, --text-faint.
• Status literals swept to semantic tokens: #3fb950/#238636 → var(--green), #d29922 → var(--yellow), #f85149 → var(--red), #8b949e/#484f58 → var(--text-muted)/var(--text-faint); the rgba(...,.15) pill backgrounds became color-mix(in srgb, var(--token) 15%, transparent).
• .spine-name is now explicitly var(--text-strong) — dark-on-light in light, light-on-dark in dark.
• Dark theme stays complete: every token used has a value in the dark block; zero color literals remain outside a comment.
• Presentation only — no logic, queries, or markup semantics changed.

Verification

• bunx tsc --noEmit -p . — clean.
• bun test src/__tests__ --test-name-pattern "docs|status" — 71 pass, 0 fail (103 skip).

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