Unified NL search Phase 2: /photos/search/unified endpoint

Composes the two existing engines (Path A orchestration):
- Translate NL -> StructuredQuery via local LLM, respecting LLM_BACKEND
  (resolve_backend(Local) -> ollama or llama-swap; no hybrid).
- Forward-geocode the place name into a gps circle.
- Structured filters (tags/EXIF/geo/date/media) build a candidate set of EXIF
  rows; CLIP ranks within it, joined by content_hash. Degenerate cases match
  existing behavior: semantic-only -> plain CLIP; filters-only -> date-sorted.
- Echoes the interpreted query (incl. resolved place) for editable client chips.

Refactor: extracted reusable cores from clip_search (score_photos, resolve_hits,
parse_library_scope, score_error_response) shared by both endpoints. Removed the
Phase 1 allow-until-wired attributes now that nl_query + geo are consumed.

fmt + clippy clean; 23 backend tests pass (7 geo, 12 nl_query, 4 unified).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib.rs

@@ -35,6 +35,7 @@ pub mod tags;
 #[cfg(test)]
 pub mod testhelpers;
 pub mod thumbnails;
+pub mod unified_search;
 pub mod utils;
 pub mod video;