* style(settings): align settings pages with the popup design

Bring the six settings pages to the popup's visual language without
changing settings, defaults, saved values, CLI calls, or tab order.

Helper text uses one small secondary style at the 0.7 step and aligns
with the text of the check box or radio button it explains. A shared
flat DisclosureButton replaces three disclosure styles; the arrow
carries the state and assistive technology still reports it as a
checkable toggle. Panel's quota, order and visibility options stack
their labels in the main field column, so expanding them no longer
shifts the form. The CLI release notification option is indented under
its parent, which FormLayout previously ignored.

Providers shows the selected provider on one borderless surface with
the popup's identity tile, quiets the Enabled/Disabled group labels,
and wraps long setting names and values. Popup groups provider order
and Overview providers under Providers. Diagnostics runs redacted
diagnostics from a Provider diagnostics form section instead of a
separately aligned block. Notifications explains the unavailable
incident option directly below it.

The smoke runner gains --theme and --language, captures every settings
page including Providers with a long synthetic roster, narrow pages
with larger text, and Providers/Diagnostics error states. Panel matrix
reuses the runner's palette helper.

Documentation impact: CHANGELOG Unreleased, usage guide settings and
Providers sections, development guide smoke runner options and
scenarios, the settings decision record and its docs index entry. The
translation template gains source references only; no strings changed.
TODO.md is unaffected.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* chore: add temporary settings review captures

Synthetic before/after captures referenced by the pull request body.
Removed in the next commit, so the squash merge does not include them.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* chore: remove temporary settings review captures

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* docs(smoke): state that share-usage captures stay dark

--theme applies to every selected scenario except the README and
share-usage captures, which the runner always stages with Breeze Dark.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>