fix: bump compiler version to v3 for runuser entrypoint

The previous compiler_version v2 already produced an image tag
(3d34c636) for the su-based fix. Images built under v2 still had the
broken su entrypoint that exited immediately. Bump to v3 so the runuser
change forces a fresh image build with the corrected privilege drop.

Quality gates:
- pytest tests/unit: 219 passed

apps/api/src/services/build/manifest_compiler.py

@@ -582,7 +582,7 @@ def compute_image_tag(tool_name: str, manifest: dict) -> str:
     Returns:
         Docker image tag string.
     """
-    compiler_version = "v2"  # bump when compile_dockerfile/entrypoint/compose change
+    compiler_version = "v3"  # bump when compile_dockerfile/entrypoint/compose change
     canonical = json.dumps(manifest, sort_keys=True, separators=(",", ":"))
     hash_suffix = hashlib.sha256(
         f"{compiler_version}:{canonical}".encode()