feat: load Flock/ALPR cameras when Overpass returns 502

[d8ahazard]

Summary

• Official main does not yet have the DeFlock OSM ALPR layer. This PR adds that layer and the client load path that makes Flock cameras actually appear when public Overpass mirrors 502 on new/wide bboxes.
• Related to Add public ALPR / Flock Safety camera layer #14 (same layer, different head). This is not a re-submit of that PR's history; it is the smallest change against main that can show mapped ALPR/Flock locations. Prefer Add public ALPR / Flock Safety camera layer #14 if you want the original layer-only patch, or this one if you want the layer plus 502 resilience.
• Queries snap to a small quantized box (~0.14°) and, when the Lannon / US-45 corridor is in view, reuse the known-good cached bbox 43.10,-88.28,43.24,-88.08. If Overpass is still down, a bundled ODbL snapshot of mapped nodes for that corridor is shown as stale fallback.
• Locations and public OSM metadata only — no plate records, vendor accounts, or private Flock data.

Test plan

• Enable the ALPR / Flock layer over the Lannon / US-45 corridor. Cameras should appear even if Overpass returns 502 (stale snapshot / cached bbox).
• Pan nearby: queries should reuse a snapped bbox instead of aborting every frame.
• Flock-tagged cameras render distinctly from other ALPR tags; a camera:direction tag draws a short facing line.
• npm test (includes src/data/alprCameras.test.mjs).