fix: add package marker comment to __init__.py template files

The 12 __init__.py files in src/assets/python/ were 0-1 bytes (empty or
single newline), which made them fragile through the Handlebars rendering
pipeline and npm tarball distribution. This caused "works in Docker,
breaks locally" issues for editable installs, pytest, and mypy.

Replace empty content with a `# Package marker` comment so the files
survive template rendering and packaging reliably.

Author: tejaskash

src/assets/__tests__/__snapshots__/assets.snapshot.test.ts.snap

@@ -934,7 +934,7 @@ if __name__ == "__main__":
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/autogen/base/mcp_client/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -961,7 +961,7 @@ async def get_streamable_http_mcp_tools() -> List[StreamableHttpMcpToolAdapter]:
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/autogen/base/model/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -1293,7 +1293,7 @@ if __name__ == "__main__":
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/crewai/base/model/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -1653,7 +1653,7 @@ if __name__ == "__main__":
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/googleadk/base/mcp_client/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -1677,7 +1677,7 @@ def get_streamable_http_mcp_client() -> MCPToolset:
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/googleadk/base/model/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -1901,7 +1901,7 @@ if __name__ == "__main__":
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/langchain_langgraph/base/mcp_client/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -1929,7 +1929,7 @@ def get_streamable_http_mcp_client() -> MultiServerMCPClient:
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/langchain_langgraph/base/model/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -2256,7 +2256,7 @@ if __name__ == "__main__":
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/openaiagents/base/mcp_client/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -2279,7 +2279,7 @@ def get_streamable_http_mcp_client() -> MCPServerStreamableHttp:
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/openaiagents/base/model/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -2524,7 +2524,7 @@ if __name__ == "__main__":
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/strands/base/mcp_client/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -2544,7 +2544,7 @@ def get_streamable_http_mcp_client() -> MCPClient:
 `;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/strands/base/model/__init__.py should match snapshot 1`] = `
-"
+"# Package marker
 "
 `;
 
@@ -2701,7 +2701,10 @@ packages = ["."]
 "
 `;
 
-exports[`Assets Directory Snapshots > Python framework assets > python/python/strands/capabilities/memory/__init__.py should match snapshot 1`] = `""`;
+exports[`Assets Directory Snapshots > Python framework assets > python/python/strands/capabilities/memory/__init__.py should match snapshot 1`] = `
+"# Package marker
+"
+`;
 
 exports[`Assets Directory Snapshots > Python framework assets > python/python/strands/capabilities/memory/session.py should match snapshot 1`] = `
 "import os

src/assets/python/autogen/base/mcp_client/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/autogen/base/model/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/crewai/base/model/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/googleadk/base/mcp_client/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/googleadk/base/model/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/langchain_langgraph/base/mcp_client/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/langchain_langgraph/base/model/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/openaiagents/base/mcp_client/__init__.py

@@ -1 +1 @@
-
+# Package marker

src/assets/python/openaiagents/base/model/__init__.py

@@ -1 +1 @@
-
+# Package marker