feat(docs): scaffold docusaurus next site (phase 1)

[pratyush618]

First phase of the docs migration off Zensical. Sets up docs-next/ (Docusaurus 3.10.1 + TypeScript) alongside the existing Zensical site. The Zensical site at docs.byteveda.org/taskito keeps shipping unchanged; nothing is removed or repointed in this PR.

What's in here

docs-next/ — Docusaurus 3.10.1 scaffold customised for Taskito:

• Title / tagline / favicon / GitHub edit URL
• url: https://docs.byteveda.org, baseUrl: /taskito/ (so cutover preserves existing URLs)
• colorMode.defaultMode: dark (matches the brand)
• Blog disabled (blog: false) — we're docs-only
• 5 sidebars: gettingStartedSidebar / guidesSidebar / architectureSidebar / apiReferenceSidebar / moreSidebar — all autogenerated from folder layout
• Navbar: 5 top-level docSidebar links + a More dropdown (Examples / Comparison / FAQ / Changelog) + GitHub icon
• markdown.hooks.onBrokenMarkdownLinks: 'throw' (Docusaurus v4-ready shape; the deprecated top-level field is gone)
• Prism additionalLanguages: rust, toml, bash, yaml, json, python

IA skeleton (33 files, all stubs that say "Phase 1 stub — content port pending"):

• getting-started/ × 3 (installation, quickstart, concepts)
• guides/ × 9 sub-categories (core, reliability, advanced-execution, operations, observability, resources, workflows, integrations, extensibility) — folds in three formerly-top-level Zensical sections (Resources, Workflows, Integrations) per the approved IA
• architecture/overview.mdx
• api-reference/overview.mdx
• more/ × 4 (examples, comparison, faq, changelog) — collapses Zensical's awkward "Changelog" + "Changelog Archive" split

Landing page — minimal Taskito version of src/pages/index.tsx and HomepageFeatures (3 cards: Brokerless / Rust-powered / Python-native). Phase 5 does the real visual polish.

.github/workflows/docs-next.yml — build + typecheck on PR (path-filtered to docs-next/**). No deploy step yet — cutover lives in phase 7.

What's NOT in here (next phases)

• Content port (phases 2–4) — actual prose moved from docs/ into the stubs
• API reference component (<APIMethod> — phase 3)
• Landing page polish + shadcn-style components (phase 5)
• LLM-friendly routes (/llms.txt, /raw/[...slug] — phase 6)
• Hosting / DNS cutover and Zensical decommission (phase 7)

Test plan

• pnpm install --frozen-lockfile — clean
• pnpm typecheck (i.e. tsc) — clean
• pnpm build — [SUCCESS] Generated static files in "build", zero warnings
• git status --untracked-files=all after install — node_modules / build / .docusaurus all stay out of the index (Docusaurus's own .gitignore handles them)
• CI: new Build Docs (Next) job passes on this PR
• Manual smoke once merged: spin up pnpm --dir docs-next start locally and confirm all 6 nav buckets resolve, the dropdown opens, dark mode is default

[pratyush618]

Switching to Fumadocs after revisiting the GH Pages constraint — Next.js static export works fine and the LLM-readability + MDX-with-shadcn wins are worth the swap. Replacement PR coming.