chore(main): release 0.15.0

[github-actions]

🤖 I have created a release beep boop

0.15.0 (2026-06-18)

Features

• built-in engine onboarding, model downloads, Settings providers, and default flip (#219) (171a6a3)
• bundled engine runner and model library (#217) (faa82ca)
• OpenAI-compatible /v1 client and provider routing (#218) (25fe634)
• restore the Providers setting reverted by #208 (#215) (5a5310f)

Bug Fixes

• ad-hoc sign local macOS builds so TCC grants apply (#229) (5c3a2df)
• fetch llama-server sidecar before lint in nightly release (#235) (d039999)
• gate overlay activation during onboarding to prevent window collapse (#233) (b111b1c)
• onboarding permission loop on local macOS builds (#230) (5c3a2df)
• persist onboarding progress so relaunch can't bounce permissions (#229) (a0ecbbb)
• regain overlay focus after defocus via hover-activate tracking area (#234) (dec7535)

Reverts

• restore onboarding permission-revocation detection (#231) (#232) (1f8a121)

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