Add component_area_min and component_photos_n params to fly_select

[NewGraphEnvironment]

Problem

ensure_components = TRUE seeds one photo per disconnected AOI polygon regardless of size. In practice:

• Tiny sliver polygons from union operations waste a dedicated photo
• Large components may need more than one seed photo to get meaningful initial coverage

Proposed Enhancement

Two new parameters for fly_select():

• component_area_min — minimum component area (m²) to seed. Components below this threshold are skipped during seeding (the greedy loop may still catch them). Requires real-world experience to determine a sensible default.
• component_photos_n — number of seed photos per component (default 1). For large components, seeds multiple photos ranked by intersection area before the greedy loop starts.

Both parameters only apply when ensure_components = TRUE and mode = "minimal".

Notes

The existing ensure_component_coverage() already computes component geometry and intersection areas, so both parameters are low-cost additions to the current loop.

Relates to #12