Add mobile model profile launch picker

[subhangR]

Summary

• Replace the freeform run-model field with provider-filtered server model profiles and a Custom fallback.
• Add provider selection and Claude-only reasoning controls.
• Send canonical launchConfig on mobile session spawn, with the server deriving the legacy agent tool.
• Extend the shared picker for provider metadata and expose useModelProfiles.

Why

Mobile spawning only sent legacy agentTool and raw model values, so users had to know model IDs and could not select provider or reasoning effort.

Validation

• git diff --check
• Typecheck in the original checkout reached only three pre-existing unrelated errors.
• The isolated PR worktree has no installed mobile dependencies, so its typecheck cannot resolve Expo/React modules.