Add desktop bridge transport and RAW import support

[Shiva108]

What changed

• adds the desktop bridge transport and RAW file import support
• adds unit tests for OpenRouter request serialization and signal alchemy behavior
• fixes the command parsing and executor tests so the unit test task passes again
• moves the OPENROUTER_DEFAULT_MODEL default into tracked Gradle config and stops tracking local.properties

Why

The feature commit added a new OpenRouter default via local.properties, but that file is machine-local and should not be versioned. Keeping the default in code preserves the intended behavior without shipping workstation-specific SDK paths or local config.

Impact

• desktop bridge and RAW import support are available in the app
• fresh builds default to openrouter/auto without requiring a committed local.properties
• contributors keep their own local.properties out of version control
• the unit test task is green again on this branch

Validation

• ./gradlew :app:assembleDebug ✅
• ./gradlew testDebugUnitTest ✅