Produce version 0.1.0: single-file exports and make package

Re-read the specification (§12, §13, §15) before producing the game:
Linux and Windows are the target platforms for this version. Embed
the PCK for one executable per platform, add config/version, and add
`make package` which re-exports from scratch and builds
dist/*.tar.gz, dist/*.zip and SHA256SUMS (executable + LICENSE +
READMEs + CREDITS + a short notice). READMEs updated to the real
status. Known gaps against the spec are listed in decisions.md.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitignore

@@ -1,6 +1,7 @@
 # Runtime et artefacts Godot
 .godot/
 build/
+dist/
 
 # Outillage telecharge par `make setup` (Godot, GUT), non versionne
 .godot-bin/