[pitill0]

Summary

Closes #275.

Expose the existing station discovery sources consistently across all three FluxTuner interfaces: GTK, TUI and Web.

Users can explicitly select between:

• Radio Browser — remote station discovery (default).
• Local — stations from the current local library/profile.
• All sources — combined remote and local discovery.

The existing Radio Browser search behavior remains the default for backward compatibility.

Implementation

GTK

• Add a discovery-source dropdown to the search toolbar.
• Route local and combined searches through a dedicated desktop discovery adapter.
• Invalidate pending results and clear stale selections when switching sources.
• Preserve active playback during source changes.

TUI

• Add a source selector alongside the existing search filters.
• Provide styling for all six bundled themes.
• Implement generation-based invalidation to prevent stale search results from replacing newer views.
• Avoid cancelling Textual event-processing tasks during source changes or navigation.

Web

• Add a source selector to the search form and API.
• Preserve the existing Radio Browser search and diagnostic behavior.
• Enforce authenticated user and profile isolation for local discovery.
• Handle partial availability when combined discovery encounters remote failures.
• Abort pending browser requests and invalidate obsolete results when switching sources.

Core

• Introduce a desktop discovery adapter using worker-owned, read-only SQLite connections.
• Avoid implicit profile creation and cross-thread SQLite connection sharing.

Validation

• 1,615 tests passed.
• Ruff lint and formatting checks passed.
• Mypy passed across 107 source files.
• JavaScript syntax validation passed.
• Python compilation passed.
• Git whitespace checks passed.
• Manual smoke testing completed for GTK, TUI and Web.

Additional regression coverage includes source selection, stale-result handling, TUI concurrency, SQLite connection lifecycle, authenticated Web discovery and profile isolation.

Compatibility and scope

• Radio Browser remains the default discovery source.
• No database schema changes or migrations.
• No additional runtime dependencies.
• Existing playback behavior remains unchanged.

Merge checklist

• Implementation complete
• Local test suite passing
• Static analysis and formatting passing
• GTK, TUI and Web smoke tests completed
• GitHub CI passing
• Final PR review