Replace Mintlify with Fumadocs

[hudsonaikins]

Problem

Neural documentation depends on Mintlify configuration and automation that no longer matches the selected documentation platform.

Outcome

• add a repository-owned Fumadocs/Next.js site in docs-site/
• keep docs/ as the single authoritative content source
• provide generated navigation, search, responsive layouts, and a Neural visual shell
• replace Mintlify CI with locked Fumadocs typecheck and production-build validation
• remove Mintlify-only workflows, configuration, dependencies, and stale automation plan
• keep deployment, hosting, and DNS outside this PR

Acceptance Criteria

• all documentation pages compile through Fumadocs
• /docs, Getting Started, Data Collection, and Trading Quickstart render on desktop and mobile
• search and mobile navigation work
• no Mintlify references remain in the candidate
• documentation and example validators pass
• full Python regression suite passes
• Fumadocs dependencies install from the committed lockfile in a fresh worktree
• all review threads addressed and resolved

Validation

Exact head: 818263c3cf5daa2cb05f3324636638606872dee8

• uv lock --check
• uv sync --extra dev --dry-run
• uv run python scripts/validate_docs.py
• uv run python scripts/validate_examples.py
• uv run ruff check .
• uv run pytest -q — 111 passed, 6 skipped
• bun install --frozen-lockfile
• bun run typecheck
• bun run build — 41 generated routes
• Playwright desktop/mobile route, search, sidebar, console, and overflow checks

Residual Risk

Existing documentation coverage and example-quality warnings remain advisory and predate this migration. Hosting selection, production deployment, DNS, and live monitoring require separate approval.

Plane mapping: none identified; no work-item identifier invented.

[github-actions]

📚 Documentation Status

✅ Documentation changes detected

• Documentation structure validated
• Links checked for broken references
  ✅ README changes detected

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