chore - add Prismplane docs site and strict docs CI (#9)

[dannymeijer]

Summary

This PR turns the existing IncQL documentation into a strict MkDocs Material site and establishes Prismplane as the shared documentation direction for IncQL and future Encero projects. It includes the responsive landing page, the architecture narrative and technical query trace, the Part-based IncQL Book, clearer site navigation, lifecycle-based RFC folders, and a searchable RFC Context Reader with controlled many-to-many tags.

Closes #9.

Deployment note: this PR intentionally remains draft and is not being merged. For design and navigation QA, the docs can be published manually from feature/9-docs-ci through the existing workflow_dispatch path. The current review build is available on GitHub Pages.

Type of change

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

Area(s)

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

Key details

• Landing and architecture: adds a responsive IncQL launch page, preserves the distinction between IncQL and Prism, and teaches the typed path from authoring through Prism, Substrait, execution, and attached evidence.
• Guided IncQL Book: follows one cumulative order-processing project through three expandable Parts—model the work, explain and execute it, and decide what happens next. Every chapter identifies system ownership, primary artifacts, knowable evidence, and important boundaries while keeping the complete runnable source available on demand.
• Extensible learning model: groups chapters by engineering outcome rather than a fixed global sequence, leaving room for future Parts on query syntax, streaming, multi-backend execution, and other independent or advanced paths.
• Information architecture: reorganizes navigation around Learn, Guides, Reference, Architecture, Design records, and Project while retaining ordinary Markdown fallbacks.
• RFC lifecycle: follows the Incan repository model by keeping active RFCs at the RFC root and moving terminal records into status-specific closed/ folders.
• RFC reader: generates validated reader data from RFC source files and a controlled tag catalog; supports search, lifecycle/status filters, many-to-many tag intersections, keyboard behavior, mobile master/detail views, and bookmarkable repeated tag URL parameters.
• Reusable contract: documents the source schema, generated record shape, URL behavior, AND semantics, and brand-token seam intended for later ports to Incan, Hees.ai, and other Encero sites.
• CI and docs platform: builds strictly, validates generated RFC data, and runs Python plus dependency-free Node contract tests.
• Risks: the custom landing, architecture, book, and RFC-reader layers sit on MkDocs Material. Strict builds, deterministic generation, frontend state tests, progressive-enhancement fallbacks, and responsive browser QA cover the main regression paths.

Testing / verification

• Manual verification described below

Manual verification notes:

• make docs-build: strict MkDocs build passed.
• python3 -m unittest discover -s tests/docs -p 'test_*.py': 23 tests passed.
• node --test tests/docs/test_rfc_reader.cjs: 8 tests passed.
• node --check docs/javascripts/prismplane.js.
• git diff --check.
• Book QA at desktop and 390 px mobile: all three Part summaries, current-Part chapter journeys, evidence traces, receipts, and collapsible source panels remain readable without horizontal overflow.
• Book interaction QA: only one Part opens at a time, and a direct Part hash opens the requested Part.
• RFC Browser QA at desktop, the original 967 px problem width, and 390 px mobile: no horizontal overflow; tag filtering, selection, detail toggles, and keyboard traversal remain usable.
• Live Pages QA: the deployed Book contains all three Parts and the Part II accordion state switches correctly.
• Docs workflow run 29694458368 completed successfully for commit 6c64e8b.

Docs impact

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

Primary links:

• Docs site
• 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 or updated tests where they materially reduce regressions