feat: add mod editing, revision merges and secure game storage

Add immutable revisions, PGVN editor, asset replacement, merge and rebase workflows, authenticated media delivery and reachability GC. Harden the script interpreter, pin unrpyc and remove tracked build metadata. Include current compatibility checks, Naninovel import and regression tests.

backend/Dockerfile

@@ -5,8 +5,13 @@ RUN apt-get update \
     && rm -rf /var/lib/apt/lists/*
 
 # unrpyc v2 decompiles .rpyc from Ren'Py 6.18 – 8 on Python 3
-ARG UNRPYC_REF=master
-RUN git clone --depth 1 --branch ${UNRPYC_REF} https://github.com/CensoredUsername/unrpyc /opt/unrpyc \
+ARG UNRPYC_REF=3ae8334ed71a05535927dcc559663d3aca51215b
+RUN git init /opt/unrpyc \
+    && git -C /opt/unrpyc remote add origin https://github.com/CensoredUsername/unrpyc \
+    && git -C /opt/unrpyc fetch --depth 1 origin ${UNRPYC_REF} \
+    && git -C /opt/unrpyc checkout --detach FETCH_HEAD \
+    && test "$(git -C /opt/unrpyc rev-parse HEAD)" = "${UNRPYC_REF}" \
+    && printf '%s' "${UNRPYC_REF}" > /opt/unrpyc/REVISION \
     && rm -rf /opt/unrpyc/.git
 
 WORKDIR /app