Upgrades `docs/conf.py` and the docs dependency stack to Starbase's current 'Sphinx Stack 2.0' template, extracted ahead of the broader Starbase merge (#270) since it's a large, independently-mergeable, template-derived change. ## What's changing - `canonical-sphinx[full]~=0.2` -> `canonical-sphinx~=0.6` (extensions it used to bundle via the `[full]` extra are now declared explicitly). - New `docs-sphinx-stack` dependency group (sphinx-design, sphinx-notfound-page, sphinx-rerediraffe, sphinx-sitemap, sphinx-llm, sphinx-related-links, sphinx-roles, sphinx-terminal, sphinxcontrib-jquery, sphinxext-opengraph, vale, etc.), scoped to `python>=3.10` since `canonical-sphinx>=0.6` requires it. - `docs/conf.py` rewritten to match: sitemap config, redirects (`docs/redirects.txt`, new, currently empty), llms.txt generation config, updated `html_context`/theme options, new extensions list. - Dropped the dead `sphinx-toolbox.github` config (`github_username`/`github_repository`) — also removed independently in #274. - Kept `explanation/index.rst` in `exclude_patterns`, since this PR intentionally doesn't touch `docs/index.rst`'s toctree structure (that's part of the wider Starbase docs restructuring in #270). - `uv.lock` regenerated (kept the existing file as a base rather than deleting it, to avoid unrelated floating-dependency drift). ## Validation Ran `make format`, `make lint-docs`, `make docs`, `make test-fast` — all green, using a fresh isolated venv sync to match what a clean CI checkout produces. 🤖 [BEEP BOOP, A BOT WROTE THIS COMMENT - Claude Sonnet 5, GitHub Copilot CLI]