The provider, rotation and autoselect detail forms were single huge forms.
Split them into collapsible sub-panels so only basic settings stay visible:

- Shared subPanel()/toggleSubPanel() helper + CSS in base.html, defined
  before the content block so page scripts can call it during first render.
- Providers: basic fields visible; Authentication, Pricing & Tiers, Rate
  limits & defaults, Feature Overrides, Native Caching, Models as panels;
  each model has basic config visible + an Advanced sub-panel.
- Rotations: basic visible; Advanced configuration panel; one panel per
  provider (model-count + usage badge); one panel per model with an
  Advanced sub-panel.
- Autoselect: basic visible; Classification, Feature Overrides, Default
  settings panels; one panel per available model.
- Panel open/close state and top-level item expansion persist via
  sessionStorage, so they survive navigation within a session.

Bump version to 0.99.75.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>