fix(mobile): restore a removed language on Starter instead of a dead end; Tell me survives a reload (M-05, M-15)

[navidshad]

What

Follows server #138.

• Never stuck on first run. On Starter, a removed language keeps its place for 30 days, so adding any other language returns upgrade_needed. A Starter learner who removed their only language lands on first run. There, and in Add a language, the switcher and Languages, the plan card now reads "Starter includes 1 language, and your German is kept until 14 November…". It offers Restore German first (add-language brings the language and its data back) and See plans second. The language grid is hidden then, because any other choice would be refused.
• LanguageState.slotsUsed counts removed languages on Starter only, which matches the server. "x of y used" uses it.
• Tell me survives a reload: get-language-state now returns interests, and Add a language shows "Got it" for them.
• Coming later: Portuguese comes from the capabilities with enabled: false and is listed there (already handled; now covered by a test).
• Fake server: returns interests, and holds a removed language's place on Starter, so only a restore gets in.

Tests

• flutter test (app) 92 pass. New tests cover:
  • a first run after removing the only language: Restore → German Today;
  • a stale phone state that reloads into the Restore card;
  • Tell me remembered from interests, Portuguese under Coming later, and undo;
  • the Starter-only place rule.
• dart test (api) 64 pass, now also reading interests and checking slotsUsed.
• flutter analyze clean.

🤖 Generated with Claude Code

[github-actions]

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