Initial commit: Deepwave Phase 1 - auth scaffolding

Spotify-like Navidrome client scaffold with Hilt DI, a Subsonic API
client (token auth, base-URL rewriting), encrypted single-server
credential storage (DataStore + Tink/Keystore), and a login/session
flow gating Compose Navigation between Login and a placeholder Home
screen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/caches
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+/.idea/navEditor.xml
+/.idea/assetWizardSettings.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties