feat(ariadne): add extraction preparation script

src/ariadne/README.md

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+# Ariadne
+
+Ariadne prepares Ren'Py game source for later analysis.
+
+## Bazel shape
+
+Keep project-owned source under `src/ariadne/`. Keep game-derived files local and ignored under
+`src/ariadne/output/`.
+
+The first target is a shell entry point:
+
+```sh
+bazel run //src/ariadne:extract_and_decompile -- \
+  --game-root /path/to/game-install
+```
+
+The script defaults to `<workspace>/src/ariadne/output`.
+This path stays stable when you run the command from inside `src/ariadne`.
+Use the game installation directory as the game root.
+One run processes all installed season directories.
+If `rpycdec` is not available, the script uses `extract-tools.nix` to enter a Nix shell.
+
+Keep the script as a thin orchestration layer.
+Bazel owns stable inputs and wrappers.
+Keep large game files and recovered output outside the build graph.