Support transparent full-canvas HD rounding and rebuild runtimes

Accept strict common-scale integer rounding for complete transparent PNG canvases while retaining source-aware alpha checks and existing opaque/exact cache identities. Add separate cache identity for newly eligible rounded transparent frames and matching Rust/Python regression coverage. Bundle rebuilt Linux and GNU Windows executables against the unchanged reviewed4978 asset pack.

Validation: 31 Rust HD tests, 7 Python audit tests, and 341 portable tests passed; zero failures. Original-data integration validated all4978 remasters at scales1–4 with bounded caches. Three fresh software SDL1920x1080 menu/mission captures are pixel-identical to published controls. Windows PE/dependency and complete shared data hashes verified; fresh Wine asset and45-mod validation passed. Artwork geometry remains independently reviewed; no held candidate is admitted by the format change.

runtime-windows-manifest.json

@@ -37,7 +37,7 @@
     ]
   },
   "files": {
-    "bin/raptor-rust.exe": "ad2ee7f5cc8e90ea371eccf2a509cd99263c6c880a6d42e2886cdc017c24561b",
+    "bin/raptor-rust.exe": "546f18a1e0f5df3d601058ffbd63e74190505878fa677a75c310ef1ff5c9dd51",
     "bin/SDL2.dll": "53e8fa7e9ed43c30bd650c39396f0d9d2067d2fff0b926c9433b75202592e4aa",
     "bin/SDL2-WINDOWS-LICENSE.txt": "97f35b302b361680ec1e891e95d2d52097bb95abff361434916d99dc1305f127",
     "run.cmd": "b007382d9ed3560191856514a9ebd4e429801fc25428840e304bb297f3553269"