Docs: adopt ColorCraft Technical English and refresh product documentation

[Artsen]

Summary

• Add ColorCraft Technical English, a project-specific controlled technical-writing standard informed by ASD-STE100 principles.
• Refactor the documentation into canonical product, setup, user, architecture, color-analysis, API, runtime, persistence, testing, troubleshooting, brand, and contribution guides.
• Verify workflow labels, API contracts, runtime variables, extraction and relationship calculations, export behavior, persistence, and security boundaries against the current source and tests.
• Keep this change documentation-only.

Base main commit: f58e6417c84feecf86cecd76a7049711d6f94036

Governance

ColorCraft Technical English is informed by ASD-STE100 principles. ColorCraft does not claim formal ASD-STE100 compliance. No ASD-STE100 controlled-dictionary content was copied.

The standard defines three application levels, procedure and error patterns, required domain distinctions, and preferred ColorCraft terminology. Application code, API schemas, and tests remain the source of truth for behavior.

Documentation structure

New canonical documents:

• docs/writing-style.md
• docs/color-analysis.md
• docs/user-guide.md

Updated canonical documents:

• README.md and docs/README.md
• docs/getting-started.md
• docs/architecture.md
• docs/api-contracts.md
• docs/runtime-configuration.md
• docs/persistence-and-privacy.md
• docs/testing.md
• docs/troubleshooting.md
• docs/brand-system.md
• CONTRIBUTING.md

Removed obsolete duplicate documents: docs/api.md and docs/user-workflow.md.

Product and technical corrections

• Replace stale linear/scrolling workflow material with the current Create, Review, Export, and Library workflow.
• Document the exact Review tabs: Overview, Harmony, Contrast, and Suggestions.
• Remove obsolete controls and do not document palette reordering because the current UI has no reorder control.
• Do not retain a speculative roadmap or list implemented exports, tests, or OpenAPI support as future work.
• Document current browser-side CSS custom properties, schema-version-1 JSON, Tailwind theme colors, and SVG swatch-sheet exports, including Copy and Download.
• Correct representative-color documentation to the sampled RGB medoid nearest each LAB cluster center; remove obsolete LAB median/LAB-to-RGB claims.
• Document exact upload, decoded-pixel, resize, sample, seed, KMeans, transparency, population, ordering, relationship, fit, contrast, invalidation, schema, and escaping behavior.
• Correct runtime documentation to use VITE_COLORCRAFT_API_URL; remove the nonexistent VITE_API_URL and COLORCRAFT_NO_BROWSER claims; state that the launcher does not open a browser.
• Consolidate exact current camelCase contracts and routes in docs/api-contracts.md, including FastAPI /docs and /openapi.json.
• Replace stale contribution setup and validation commands with the Python 3.11 and pinned pnpm 9.15.9 workflow.

The task brief described palettes as entirely session-only and stated that no saved-palette library existed. Current main includes the merged IndexedDB Palette Library. These documents therefore follow current source truth: saved palette records persist in IndexedDB, while source-image bytes, analysis, suggestions, unsaved changes, and previews remain session-only. Browser history stores the active view and Review tab, not palette data.

Application copy follow-ups

No production copy changes are included. Confirmed follow-ups:

• Create advertises and validates “up to 15 MB,” but the API enforces 10 MB.
• The Local only status badge is ambiguous when trusted LAN access is configured and does not by itself mean private, secure, offline, or persistent.
• The shell description says ColorCraft can “validate color palettes,” although relationship and contrast analysis cannot validate aesthetic quality or complete accessibility.
• Suggestions exposes Mood and factual-sounding subjective claims such as “maximum contrast and visual energy”; this conflicts with the measured-versus-recommended distinction.

Screenshots

No screenshots changed. The README references the current curated Review and Palette Library screenshots. The older committed screenshot set is not referenced by current documentation, so this PR does not replace it or commit temporary browser-review output.

Validation

Passed:

• backend\.venv311\Scripts\python.exe -m pytest tests/test_docs.py -q — 2 passed; Markdown links and curated image paths verified.
• backend\.venv311\Scripts\python.exe -m compileall -q backend
• corepack pnpm@9.15.9 exec prettier --check . --end-of-line auto — all matched frontend files pass formatting.
• All remaining check.py stages — ESLint, TypeScript, 67 Vitest tests with coverage, production build, Ruff format/lint, mypy, 59 pytest tests with coverage, and 2 Playwright/axe workflows passed.
• git diff --check

On this Windows checkout, the unmodified frontend working files are converted to CRLF by core.autocrlf=true, so the unmodified first check.py Prettier step reports 68 line-ending-only warnings. The repository index is LF, the equivalent Prettier check with --end-of-line auto passes, and GitHub Actions checks the LF repository content.

Scope confirmation

• No runtime behavior changed.
• No backend or frontend production code changed.
• No API, algorithm, export, persistence, runtime configuration, dependency, test, or UI-copy behavior changed.
• No private paths, credentials, virtual environments, node_modules, build output, temporary screenshots, uploaded images, or other local/generated files were committed.

Ready for review. Do not merge as part of this task.