Migrate audit-logger: it builds itself now

The first module moved onto the new build process. It named a placeholder digest
nothing could produce, so it only ever worked where somebody had pre-built its
image by hand. It names the two shared bases instead, and the mesh builds it.

Chosen first deliberately: it requires nothing, nothing requires it, and an
audit trail of every event on the mesh is the thing most worth having while
modules are being moved one at a time.

modules/audit-logger/Dockerfile

@@ -0,0 +1,33 @@
+# audit-logger's runtime: the shared runtime image, carrying this module's compiled code.
+#
+# **Built from this module's own directory and nothing else.** The toolkit is in the base image, so
+# nothing is copied out of a neighbouring checkout — which is what lets the mesh build this from a
+# repository and a path (novox/hq ADR 0069) rather than only on a workstation that happens to have
+# the siblings laid out beside it.
+
+# Two bases, named rather than pinned: the image this is COMPILED in, and the image it RUNS in.
+# They are different images on purpose — the first carries a compiler and the second must not, or
+# every running container would carry one it never invokes. The mesh answers both with the copies it
+# holds, because a fingerprint written here would name one particular copy and no other mesh has it
+# (novox/hq issue 044). Declared in module.json's `build.on`; deliberately no defaults, so a build
+# nobody told stops here and says which module to build first.
+ARG BUILD_BASE
+ARG RUNTIME_BASE
+
+FROM ${BUILD_BASE} AS build
+# Compiled under /app/modules so `@novox/mesh-sdk` resolves upward into the base's own
+# node_modules — the module is compiled against exactly the toolkit it will run against.
+WORKDIR /app/modules/audit-logger
+COPY . .
+# The compiler is invoked by its real path rather than through node_modules/.bin, whose entries are
+# symlinks to a launcher that requires its library relatively — resolved away when the base image
+# was assembled.
+RUN node /app/node_modules/typescript/bin/tsc audit.ts index.ts \
+      --module NodeNext --moduleResolution NodeNext --target ES2022 --outDir dist
+
+FROM ${RUNTIME_BASE}
+COPY --from=build /app/modules/audit-logger/dist /app/modules/audit-logger/dist
+# **Served, not run.** This subscribes on import, and the serve mode binds the broker before it
+# imports anything — `run` exists for a step that works offline and exits, and would leave this
+# with nothing to subscribe to.
+ENV MESH_TOOL_MODULES=/app/modules/audit-logger/dist/index.js