[pitill0]

Summary

Closes #273.

Introduce read-only, profile-scoped local station discovery as the first implementation phase following the architecture investigation in #256.

Changes

• Add fluxtuner/core/local_station_search.py with an explicit search_local_stations() interface.
• Discover stations belonging to the selected profile through favorites and playlist membership.
• Deduplicate stations through the existing shared station identity.
• Support searches by display name and tags, with deterministic relevance ranking.
• Support country, minimum bitrate and result-limit filters.
• Preserve useful MIME metadata for player compatibility.
• Require an existing, explicit profile ID; never fall back to another profile.
• Restrict result metadata to known shared station fields and favorite metadata belonging to the selected profile.
• Support genuinely read-only SQLite connections without modifying transaction boundaries.

Validation

• 24 new local discovery tests passing.
• Full suite: 1,561 passed, 7 skipped.
• Ruff: passed.
• Python compilation: passed.
• Targeted mypy: passed.

Full-project mypy currently reports nine errors in three unrelated files (theme_runtime.py, tui.py and web/app.py). These were reproduced against an unchanged copy of the base commit and are not introduced by this PR.

Scope and follow-ups

• No SQLite schema changes.
• No changes to existing Radio Browser search behavior.
• No GTK, TUI or Web source selectors.
• No Brynse changes.
• Combined discovery is tracked by Compose opt-in local and Radio Browser station discovery #274.
• Interface integration is tracked by Add discovery-source selection to GTK, TUI and Web #275.
• Persistent multi-source provenance is tracked by Design and persist multi-source station provenance #276.

Note: Existing shared station metadata does not reliably encode the original ownership or provenance of every field. This PR protects profile-specific search results without redesigning historical station persistence; that broader concern remains part of #276.