feat(prompts): align with Claude Design conventions (empty EDITMODE, 9-token palette, 2-font default, animation cap, Fraunces for marketing)

[hqhq1025]

Five small content updates that align our system prompt with patterns extracted from real Claude Design output (research docs §1.2, §2, §6, §11.3, §11.4).

Reopened after #109 squash-merge auto-closed the original (#110). Rebased cleanly onto current main.

Changes

1. EDITMODE protocol — empty {} block valid (research §11.4). Documents that an empty marker block is a valid signal to the host that the artifact is tweak-aware.
2. Design methodology — token density (research §1.2). New subsection: aim for 9 ± 3 oklch tokens per artifact, declared as a flat object.
3. Craft directives — Typography ladder (research §2). Default to two font families (display + workhorse sans). Mono is on-demand only — not part of the default ladder.
4. Craft directives — Animation budget (research §6). New subsection capping CSS keyframes at four named animations: fadeUp, breathe, pulse-ring, spin, with staggered animation-delay.
5. Progressive disclosure — Marketing font hint (research §11.3). New marketingFontHint Layer 2 section + routing in composeCreateProgressive. Marketing/landing/case-study prompts now surface a Fraunces preference reminder (~150 chars).

Tests

• +1 marketing prompt includes Fraunces hint
• +1 dashboard prompt does NOT include Fraunces hint
• Existing drift test auto-handles the new section (PROMPT_SECTIONS / PROMPT_SECTION_FILES both updated; one new marketing-font-hint.v1.txt)
• 161 → 163 tests, all green

Verification

• pnpm --filter @open-codesign/core test ✅ 163/163
• pnpm --filter @open-codesign/core typecheck ✅
• pnpm exec biome check packages/core/src/prompts/ packages/core/src/generate.test.ts ✅

PRINCIPLES §5b checks

• Compatibility ✅ — additive only, no schema/contract changes
• Upgradeability ✅ — sections registered in PROMPT_SECTIONS map, drift test enforces .txt/TS parity
• No bloat ✅ — marketing hint only ships when keyword matches; budget for matched dashboard prompt still <25 KB
• Elegance ✅ — content edits + one routing line; no abstractions added

[github-actions]

Findings

• No high-confidence issues found in added/modified lines.

Summary

• Review mode: initial
• No blocker/major/minor/nit findings attributable to this diff.
• Residual risk: docs/VISION.md and docs/PRINCIPLES.md are not present in this checkout (Not found in repo/docs), so hard-constraint verification was limited to repository-visible constraints and changed files.

Testing

• Not run (automation)

open-codesign Bot