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/tsconfig.json

@@ -9,6 +9,7 @@
     "target": "ES2021",
     "sourceMap": true,
     "outDir": "./dist",
+    "rootDir": "./src",
     "baseUrl": "./",
     "incremental": true,
     "skipLibCheck": true,
@@ -17,5 +18,6 @@
     "strictBindCallApply": false,
     "forceConsistentCasingInFileNames": false,
     "noFallthroughCasesInSwitch": false
-  }
+  },
+  "exclude": ["node_modules", "dist", "prisma"]
 }