Summary

This PR turns the IncQL documentation into a strict MkDocs Material site and
establishes Prismplane as its shared visual and information-architecture
direction. It combines the responsive crystal interface with a route-first
learning system, task Guides, exact Reference material, the architecture
narrative, the Part-based IncQL Book, and a searchable RFC Context Reader.

Closes #9.

Deployment note: this PR intentionally remains draft. The documentation can be
published for design and navigation QA through the existing manual
workflow_dispatch path without merging the PR.

Type of change

• Bug fix
• New feature
• Refactor / maintenance
• Documentation
• CI / tooling
• RFC (adds/updates docs/rfcs/**)

Area(s)

Select the primary areas touched (labels sync from checked lines when the triage workflow runs):

• Package & tests
• Specification (RFCs)
• Documentation
• Automation & repo config
• Other

Key details

• User-facing behavior: Adds a responsive crystal documentation shell,
  self-hosted typography and optimized brand assets; introduces newcomer routes
  for SQL, Spark/DataFrame, database, and Incan readers; organizes Guides by
  outcome and Reference by decision point; adds quickstart, read/write, join,
  troubleshooting, capability, and audience-bridge pages; and preserves the
  interactive Architecture and RFC-reader experiences on desktop and mobile.
• Internals: Uses a declarative longest-prefix navigation policy, progressive
  enhancement for the responsive drawer and Architecture tour, deterministic
  RFC catalog generation, dependency-free Node interaction contracts, local
  Manrope/Outfit assets, and WebP images with PNG fallbacks. The theme ownership
  and browser QA matrix are documented for future contributors.
• Capability truth: Current-product copy is bounded to the implemented
  IncQL authoring forms, Prism evidence, portable Substrait boundary, Session,
  and current DataFusion adapter. It does not present future backends,
  distributed execution, or cost-based optimization as shipped behavior.
• Risks: The custom presentation remains an ordered multi-file CSS cascade.
  Browser lifecycle behavior is covered by structural and pure-contract tests
  plus manual browser QA rather than an automated real-browser CI suite. Legacy
  browsers receive larger PNG fallbacks. The included quickstart is website
  content; compiler execution against Incan 0.5 is a separate validation scope.

Testing / verification

• make ci (or make fmt-check, make build, make test)
• Manual verification described below

Manual verification notes:

• make docs-build passed: 33 Python tests, 12 Node tests, RFC catalog
  validation, and strict MkDocs build.
• node --check docs/javascripts/prismplane.js passed.
• node --check docs/javascripts/crystalline.js passed.
• git diff --check passed.
• Desktop QA covered Home, Learn, Book, Guides, Reference, Architecture, and
  Design records with no broken images or horizontal overflow.
• Mobile QA at 390 × 844 covered Home, Architecture, and Design records; the
  responsive drawer works with pointer and keyboard input.
• All five Architecture boundary selections preserve the same 228 px inspector
  height.
• The RFC reader retains search, status and tag filtering, selection repair,
  keyboard behavior, mobile master/detail views, and bookmarkable URL state.
• The broad review-and-fix loop completed with six clean review slices covering
  claims, scope, test style, maintainability, architecture, and source quality.

Docs impact

• No docs changes needed
• Docs updated
• Docs follow Divio intent (tutorial/how-to/reference/explanation) where applicable

Primary links after a manual Pages deployment:

• Docs site
• Learn IncQL
• The IncQL Book
• Architecture
• RFC Context Reader

Checklist

• I kept public docs user-focused and moved internals to contributing docs when appropriate
• I avoided duplicating canonical install/run instructions in multiple places
• I added/updated tests where it materially reduces regressions