Add GET /api/map/sentinel1?bbox=... which queries Planetary Computer STAC
(sentinel-1-grd, last 7d, most recent), signs the vv/hh COG with a SAS token,
and returns a same-origin /titiler/... XYZ tile template. Cache keyed on
quantized bbox + UTC day (20 min TTL). 429 -> 429 (Retry-After), no imagery
-> 404, other upstream errors -> 502.
Self-host TiTiler on the Pi (ghcr.io/developmentseed/titiler, arm64, 1G cap,
host loopback 8001 -> container 8000) instead of titiler.xyz. nginx
/titiler/ proxy snippet routes browser tiles to it; TITILER_PUBLIC_BASE and
TITILER_INTERNAL_URL are env-driven (no hardcoded hostnames).
