[boydjohnson]

Adds reprojection to the static render: a Map can now use any EPSG code or proj string — a Minnesota map in UTM 15N, a US map in Albers — instead of only plain lon/lat.

How

PROJ 9.9.0 is built from source on every platform with libtiff and libcurl off. Alpine's and Homebrew's PROJ both pull those in (and OpenSSL behind curl) purely to read and download datum-shift grids. Without grids, a transformation that wants one uses PROJ's ballpark fallback — about a metre between WGS84 and NAD83, invisible at map scale.

A static PROJ embeds proj.db in the library (EMBED_RESOURCE_FILES, default ON for static builds), and USE_ONLY_EMBEDDED_RESOURCE_FILES stops it reading one off disk. So there's no data directory to ship, and behavior doesn't depend on the host.

With PROJ linked, mapnik classifies +proj=longlat exactly as the dynamic build does — so the projection.cpp patch is gone, one fewer edit to mapnik.

Verified locally (aarch64 linux-musl in podman, arm64 macOS)

• render_relations_projected (new) draws the fixture in EPSG:28992 and fails on a blank image, since a misprojected render still exits 0. Passes on both platforms.
• On a bare alpine:3.22 with zero proj.db files on disk, the unpacked archive renders the projected style correctly — the EPSG lookup can only have come from the embedded database. macOS also renders it with an empty environment.
• Linux and macOS projected output is byte-identical (md5 6889ae8e478fcbf382bcbca4068c2a14), and visually correct: the same Baarle boundaries in true proportions rather than lon/lat's east–west stretch.
• Existing lon/lat styles are unchanged: scale_denominator=1.92857 and md5 d48d0556925e17e872d0ac25229319d2 on both platforms, identical to v0.1.0.
• Still system-libraries-only on macOS; still fully static on Linux.

Costs

	before	after
linux-musl binary / tarball	16.5 / 10.4 MB	31.5 / 14.6 MB
macOS binary / tarball	44 / 21 MB	58 / 25 MB

Plus PROJ's ~250 TUs on a cold build; the CI cache covers repeat runs. The cache key includes cmake/**, so this PR starts a fresh (cold) cache lineage.

Licensing

PROJ (MIT), SQLite (public domain) and nlohmann/json (MIT, bundled by PROJ) — all compatible. NOTICE updated.

Build notes

• PROJ has C sources, so the static build now enables C.
• mapnik wraps PROJ_INCLUDE_DIRS in $<BUILD_INTERFACE:...>; a list splits the genex and leaks a source path into mapnik's install(EXPORT), so the config shim passes a single path.
• The release smoke test now also runs the projected render on the bare image, so every published archive proves its embedded proj.db.

Version

Bumps the project to 0.300.0 (from 0.1.0), matching the osmflat-rs versioning. release.yml requires the tag to equal project(... VERSION), so this release is v0.300.0.

Regex needed no work: Boost.Regex with ICU was already in, and .match()/.replace() filters work in v0.1.0.

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