Remaster eighteen original terrain pictures

Add the complete organic forest family and two Source-guided terrain tiles with portable reproduction tools and review evidence. Preserve existing game assets and restore fifteen referenced archival metadata files.

Validation: 157 maintained HD-tool tests; installed HD validation 5539/5539 with zero rejects; 45 mods; three 1080p SDL controls unchanged. SourceF binaries and gameplay are unchanged. Native Windows validation for the preceding 5521-picture commit passed.

README.md

@@ -82,8 +82,8 @@ are tracked in Git, along with mod definitions, scripts, SD/HD PNGs, WAVs,
 generation prompts and recipes. Build caches and local review files are excluded.
 See [repository layout](docs/repository.md).
 The engine supports original rendering and crisp 2×/3×/4× scaling, plus an
-optional HD artwork setting. The reviewed base-game pack covers **5,521 of
-5,753 original pictures**, with **232 still awaiting approval**. All 307 native
+optional HD artwork setting. The reviewed base-game pack covers **5,539 of
+5,753 original pictures**, with **214 still awaiting approval**. All 307 native
 AGX cinematic/font records remain preserved separately. Bundled mods include
 SD/HD artwork. [The HD backlog](docs/hd-backlog.md) records remaining originals,
 held drafts, reproducible derived artwork and finite review limits.