Fix pyproject.toml for templates without Python package directories

When templates have no Python package directory (include_python=no AND no
jobs/pipelines, OR lakeflow_only=yes), hatch cannot automatically detect
what to build. This causes 'uv run pytest' to fail with build errors:

  "Unable to determine which files to ship inside the wheel using the
   following heuristics: <https://hatch.pypa.io/latest/plugins/builder/wheel/#default-file-selection>"

Add conditional [tool.hatch.build.targets.wheel] configuration with
packages = ["src"] when $has_python_package_dir is false. This matches the
same logic used in __preamble.tmpl to determine directory structure.

The fix applies to:
- default-minimal template (no sample code)
- lakeflow-pipelines templates (SQL-only, no Python packages)

This ensures 'uv run pytest' works correctly in all template variants.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: lennartkats-db

acceptance/bundle/templates/default-minimal/output/my_default_minimal/pyproject.toml

@@ -8,7 +8,7 @@ dependencies = [
     # See also https://docs.databricks.com/dev-tools/bundles/library-dependencies
     #
     # LIMITATION: for pipelines, dependencies are cached during development;
-    # add dependencies to the 'environment' section of pipeline.yml file instead
+    # add dependencies to the 'environment' section of your pipeline.yml file instead
 ]
 
 [dependency-groups]
@@ -25,5 +25,8 @@ main = "my_default_minimal.main:main"
 requires = ["hatchling"]
 build-backend = "hatchling.build"
 
+[tool.hatch.build.targets.wheel]
+packages = ["src"]
+
 [tool.black]
 line-length = 125

acceptance/bundle/templates/lakeflow-pipelines/python/output/my_lakeflow_pipelines/pyproject.toml

@@ -25,5 +25,8 @@ main = "my_lakeflow_pipelines.main:main"
 requires = ["hatchling"]
 build-backend = "hatchling.build"
 
+[tool.hatch.build.targets.wheel]
+packages = ["src"]
+
 [tool.black]
 line-length = 125

acceptance/bundle/templates/lakeflow-pipelines/sql/output/my_lakeflow_pipelines/pyproject.toml

@@ -25,5 +25,8 @@ main = "my_lakeflow_pipelines.main:main"
 requires = ["hatchling"]
 build-backend = "hatchling.build"
 
+[tool.hatch.build.targets.wheel]
+packages = ["src"]
+
 [tool.black]
 line-length = 125

libs/template/templates/default/template/{{.project_name}}/pyproject.toml.tmpl

@@ -27,6 +27,15 @@ main = "{{.project_name}}.main:main"
 [build-system]
 requires = ["hatchling"]
 build-backend = "hatchling.build"
+{{- $has_python_package_dir := and (or (eq .include_python "yes") (eq .include_job "yes") (eq .include_pipeline "yes")) (not (eq .lakeflow_only "yes")) }}
+{{- if not $has_python_package_dir }}
+{{- /* Hatch can normally automatically detect the package directory,
+     * but requires an explicit setting when the package directory is empty.
+     */}}
+
+[tool.hatch.build.targets.wheel]
+packages = ["src"]
+{{- end }}
 
 [tool.black]
 line-length = 125