Add Overture Maps building data integration - #886

Complement OSM building data with Overture Maps ML-derived footprints
to fill coverage gaps in areas with sparse OSM mapping (e.g., rural
Africa, parts of Asia).

Key implementation details:
- STAC collections.parquet catalog for fast partition discovery (1 req
  instead of 512) with geographic pre-filtering
- Sparse HTTP Range requests: only download matching Parquet row groups
  (~4-5 MB each) instead of full partition files (~580 MB each)
- Source-based dedup: skip buildings whose primary source is OSM
- Spatial dedup: grid-accelerated centroid-in-bbox check against
  existing OSM buildings
- Extract height, min_height, num_floors, roof_shape, roof_material,
  roof_orientation, facade_color, roof_color, building class/subtype
- Smart height filtering: omit low Overture heights so buildings use
  the pipeline's default, keeping visual consistency with OSM buildings
- New --overture CLI flag (default on) with GUI toggle

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Resolve conflicts: keep both rotation (from main) and
no_overture (from this branch) in args.rs and gui.rs.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

- Track non-OSM building count for early-stop limit instead of total
  count (prevents premature partition processing halt in OSM-heavy areas)
- Reject rows with missing id field instead of falling back to "unknown"
  (prevents ProcessedWay ID collisions from hash convergence)
- Reject invalid WKB byte order values in parse_wkb_polygon (only 0/1
  are valid per WKB spec; other values indicate corrupt geometry)

- Replace vertex-in-bbox containment check with polygon bbox overlap
  test in building_to_processed_way. The old check dropped buildings
  that straddled the bbox boundary (edges crossing but all vertices
  outside). The new check matches the standard overlap test used by
  parse_overture_row, correctly including buildings whose footprint
  overlaps the target area regardless of vertex positions.
- Fix GUI progress bar regression: Overture fetch emitted progress
  value 4.0 after OSM parsing had already reached 14.0, causing the
  progress indicator to jump backwards. Now emits 14.5, which slots
  correctly between parse completion (14.0) and elevation fetch (14.0).

- Remove --overture/--no-overture CLI flag and conditionals — Overture
  Maps data is now always fetched as a supplemental building source.
  The error boundary in fetch_overture_buildings already degrades
  gracefully to an empty Vec on any failure.
- Clip Overture building polygons to xzbbox via clip_way_to_bbox,
  matching how OSM ways are clipped in osm_parser. Previously Overture
  buildings straddling the bbox boundary could produce out-of-bounds
  XZ coordinates.
- Fix panic in process_partition_file: add length check on the Parquet
  tail bytes returned by fetch_range before slicing. A truncated HTTP
  206 response would have caused an unrecoverable index-out-of-bounds
  panic that bypassed the Result error boundary.
- Remove redundant Bytes allocation in list_partition_files: pass
  response.bytes()? directly to SerializedFileReader instead of
  round-tripping through Vec<u8>.
- Filter out OSM-sourced buildings at collection time rather than at
  the final conversion step, reducing peak memory usage.

- Replace DefaultHasher with FNV-1a in gers_id_to_u64. Rust does not
  guarantee DefaultHasher's algorithm across compiler versions, so
  Overture building IDs (and deterministic RNG seeded from them) could
  silently change on toolchain upgrades. FNV-1a is a well-known, stable
  hash with good distribution and zero dependencies.
- Guard fetch_range against length==0: the subtraction
  end = start + length - 1 would underflow to u64::MAX, producing an
  invalid HTTP Range header. Now returns an explicit error.

When the user draws a new rectangle, edits/resizes the existing one,
deletes it, navigates via city search, or types new coordinates in the
bbox input field, the rotation angle is now reset to 0. This prevents
stale rotation values from carrying over to a completely different area.

Rotation reset flows through two funnel points:
- displayBboxInfoText: all map-originated bbox changes (draw, edit,
  delete, search, paste)
- handleBboxInput: manual text input of new coordinates