Group model picker by availability

[malmstein]

Task/Issue URL: https://app.asana.com/1/137249556945/task/1218304469640062
Tech Design URL (if applicable):
API Proposals URL(s) (if applicable): None

Description

Behind updatedPickers, the model picker groups by what the user can actually use rather than
by tier: one section of available models, a divider, then the gated ones. Gated rows get the
follow-up ellipsis because tapping one opens an upsell instead of picking a model, and rows
render the backend label as a subline.

Rows also get a 48dp minimum height, since rows without a subline were coming out around 38dp, shorter than the design and below the touch-target minimum.

The gated header names what unlocks the section: Pro when every gated model needs Pro,
otherwise the free trial when the user can still start one, otherwise a plain subscriber
header. Free trial eligibility is new in ModelState, read from Subscriptions. Copy sits in
donottranslate.xml until sign-off, and the old Plus/Pro header strings stay for the flag-off
path until the flag is retired.

Steps to test this PR

Feature 1

• With updatedPickers off, open the model picker and confirm it looks exactly as it does
  on develop: no sublines, Plus and Pro section headers
• Enable updatedPickers in the feature flag menu, force stop and relaunch
• Open the model picker and confirm available models come first with their sublines, then a
  divider, then the gated models with a trailing ellipsis
• As a free user who has never trialled, confirm the gated header reads "Try Free for 7 Days"
• As a Plus subscriber, confirm it reads "Pro Plan Exclusive", since only Pro models are
  gated for you
• As a free user who already used the trial, confirm it reads "Subscriber Exclusive"
• Tap a gated row and confirm it still opens the upsell, purchase for free users and upgrade
  for Plus

UI changes

Before	After

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[malmstein]

• Group model picker by availability #9814 👈 (View in Graphite)
• develop

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