feat(docs): polish default Redoc theme — reuse config.app.* + optional override

[PierreBrisorgueil]

Context

We mount Redoc with default visuals (Montserrat/Roboto, default sidebar, no logo). Multiple downstream projects ship public docs at /api/docs and would benefit from a polished default. This is a devkit-only enhancement — no per-project patches required.

Scope

1. Polish default theme in lib/services/express.js

Pass a theme object to redocOptions with:

• Typography: Inter (body) + JetBrains Mono (code), replacing Montserrat/Roboto
• Sidebar: tighter spacing, drop text-transform: uppercase on group items
• Code blocks: refined background, softer contrast
• Spacing: tighter rhythm
• No hardcoded brand color — keep Redoc default neutral

2. Wire existing config

Already wired: config.app.title, config.app.description. Add:

• info.x-logo from config.app.url (href) + optional config.app.logo (URL); if config.app.logo absent, no logo (no regression)

3. Optional downstream override

Deep-merge config.docs.redocTheme (if present) with devkit defaults:

const theme = _.merge({}, defaultTheme, config.docs?.redocTheme || {});

Downstream wanting brand color adds it in their own config — zero devkit edit.

4. Minimal custom CSS

≤ 30 lines for callouts/tables/blockquotes — only what theme schema can't cover. Injected via theme.customCss.

Out of scope

• Per-project branding (downstream concern via override mechanism above)
• Dark mode UI toggle (V2 if requested)
• x-codeSamples injection (per-endpoint, downstream .yml concern)

Effort

~2h impl + 1h test. Single PR.

Downstream impact

All downstream auto-benefit on next /update-stack. Backward-compat: absent config.docs.redocTheme = devkit defaults apply.

Refs

• Trawl docs V0 refonte 2026-05-20 (6 PRs trawl_node build(deps): bump snyk from 1.439.1 to 1.440.1 #1198-1203, content shipped)
• POC Scalar evaluated 2026-05-21, rejected (right panel waste on guide-heavy docs)