docs(site): unified microrobotica.org with sphinx-multiproject + PyData theme

[NicholasEhsanRoy]

Summary

Unified docs site for the three projects (MADDENING, MIME, MICROROBOTICA) deployed to GitHub Pages → `microrobotica.org`.

• Sphinx multiproject layout: one shared `conf.py`, three projects switched via `$PROJECT` env var. Subprojects pulled in as git submodules (`docs/projects/{maddening,mime}`) tracking each repo's `main`.
• PyData Sphinx Theme, `sphinx-design` cards, MyST.
• Landing page hero auto-plays both showcase videos (dipole-arm closed-loop control + MIME's de Jongh replication) immediately on entry, then a 3-card project grid.
• Videos served via `html_extra_path` from `docs/assets/videos/`, so they live with the docs source rather than sphinx's `_static/`.
• Doxygen → breathe re-wired for the MICROROBOTICA project; `make all` runs Doxygen then builds all three subprojects.
• New `.github/workflows/docs.yml` builds on PR, deploys to GH Pages on push to `main`. Submodule-aware checkout.
• `CNAME` points the deployed site at `microrobotica.org`.

Domain / TLS rollout (manual, post-merge)

1. Merge this PR — first deploy will land at `.github.io/MICROROBOTICA/`.
2. In the repo's Settings → Pages:
   • Set source to "GitHub Actions"
   • Set custom domain to `microrobotica.org`
   • Tick "Enforce HTTPS" once the cert is issued
3. At your DNS provider for `microrobotica.org`, add A records pointing the apex to GitHub Pages (185.199.108.153 / .109.153 / .110.153 / .111.153) and an AAAA for IPv6 (2606:50c0:8000::153 / :8001::153 / :8002::153 / :8003::153). Optionally a CNAME from `www.microrobotica.org` → `.github.io`.

Test plan

• `make all` builds locally with no errors (warnings only — see follow-ups below)
• `_build/html/index.html` references `videos/*.mp4` and the videos exist in the build output
• `_build/html/maddening/index.html` and `_build/html/mime/index.html` build from their submodule sources
• `docs.yml` workflow run on PR is green
• After merge: GH Pages shows the live site at the org domain, then at `microrobotica.org`

Known follow-ups

• A few warnings remain from pre-existing broken xrefs inside MADDENING (`developer_guide/documentation_standards.md` references a top-level `CONTRIBUTING`), and from empty doc subdirs in MIME — both tracked in MIME PR docs(site): scaffolding notice, per-project repo links, video fullscreen #4.
• Submodule pin for MIME advances once that PR merges; just run `git submodule update --remote --merge` from `docs/`.

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