Prepare FluxTuner 1.2.0

[pitill0]

Summary

Prepares FluxTuner 1.2.0.

Changes include:

• Add local radio stream recording to the Textual TUI and GTK4 GUI.
• Add FFmpeg stream-copy recording with real-time input pacing.
• Persist profile-scoped recording metadata in SQLite.
• Add Linux system tray integration for the GTK frontend.
• Keep playback and recording running while GTK is hidden to the tray.
• Update architecture, usage, development, smoke-test and release documentation.
• Update Flatpak/AppStream metadata and CRUX Flatpak build notes.
• Include fluxtuner.recorders in the Python package build.

Validation

• make gate
• Clean package build
• Installed-wheel smoke test
• TUI recording manually validated
• GTK recording manually validated
• FFmpeg real-time pacing validated
• GTK tray lifecycle manually validated
• Flatpak build manually validated
• Flatpak recording manually validated
• AppStream metadata validated

Closes #214
Closes #216