feat: upgrade titiler-pgstac to v3.2.0

[hrodmn]

• Upgrade titiler-pgstac from 1.9.0 to 3.2.0 and TiTiler core/mosaic/extensions from 0.24.0 to 2.3.0.
• Replace duplicated factory handlers with native routes and extensions; retain custom mosaic creation
  and storage.
• Adopt native API changes: TMS-qualified tile/TileJSON URLs, tilesize parameters, and point responses
  using assets instead of values.
• Add 307 redirects for legacy missing-TMS /mosaic and /collections URLs, defaulting to
  WebMercatorQuad; preserve query parameters and translate legacy tile scaling.
• Redirect supported legacy WMTS URLs to the new unqualified endpoint. Old plural /mosaics URLs require
  client migration; compatibility does not cover every historical route.
• Update Lambda database settings, Compose PG* variables, and migration documentation.
• Add 26 passing runtime tests. Docker image and live database integration checks remain outstanding.

resolves #135