fix(backend): compiled output was nested under dist/src, not dist/

api container crashed on boot: Cannot find module '/app/dist/main.js'.
Root cause: tsconfig.json had no rootDir, and prisma/make-admin.ts (run
separately via ts-node, never part of the Nest build) was swept into
the nest build compilation since there was no exclude either - so tsc
inferred the output root as the project root and nested everything
under dist/src/ instead of the flat dist/main.js the Dockerfile,
package.json scripts, and compose's worker command all assume.

Also excludes tsconfig.tsbuildinfo from the Docker build context - a
stale local incremental-build cache file was leaking in via `COPY . .`
(only dist/node_modules were dockerignored) and made nest build skip
emitting .js files entirely on a from-scratch container build once the
rootDir fix invalidated its cached signature.

backend/.dockerignore

@@ -1,5 +1,6 @@
 node_modules
 dist
+tsconfig.tsbuildinfo
 .env
 .env.development
 .env.production