docs: migrate to Zensical and overhaul the documentation

[tlambert03]

This moves the docs from mkdocs-material to Zensical and rewrites most of the content.

• Guide: pages on spaces, samples, channels, photometry, modalities, detectors, settings and saving. Each page describes what microsim computes at that stage, with the equations it uses.
• Interactive charts: spectra, photon budget, fluorophore saturation, crosstalk between channels, detector SNR, EMCCD excess noise, PMT gain, HyD dead time, camera noise, and confocal pinhole size. They use Observable Plot and d3.
  • Where a chart recomputes physics in the browser, that code lives in docs/javascripts/physics/, and each function names the Python it mirrors.
  • tests/test_js_physics.py checks the JS against microsim in node.
  • Spectra and presets are exported from microsim at build time (including FPbase spectra), so the site makes no API calls when it runs.
• Tutorials: plain Python and matplotlib. They are also built as notebooks, with "Open in Colab" and download buttons.
• Figures: generated at build time by scripts/make_doc_figures.py and not committed. The exceptions are the logos and one COSEM example image, which needs to download data.
• API reference: generated with api-autonav, one page per public module, with internal modules excluded. The overview page groups the main objects by topic.
• Claude skills: two skills in .claude/skills/. check-js-physics checks the JS physics for drift from microsim, and check-docs-prose checks the written text against the code.
• Source changes:
  • axis labels in OpticalConfig.plot_emission;
  • a module docstring for microsim.schema.
• CI: the docs workflow generates the figures and notebooks, runs zensical build --strict, and deploys.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.33%. Comparing base (0aea364) to head (fb31816).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
+ Coverage   88.15%   88.33%   +0.18%     
==========================================
  Files          48       48              
  Lines        3292     3293       +1     
==========================================
+ Hits         2902     2909       +7     
+ Misses        390      384       -6     

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