Add capture event transport and server-side write classification

[jspahn80134]

Summary:

• Route capture events through the existing CodeChat editor/server message path instead of a side HTTP fetch.
• Add a VS Code "CodeChat Capture" output channel for extension-originated capture events.
• Move write_doc/write_code classification into the server translation layer using parsed CodeMirror/code/doc-block structures.
• Preserve compile/save/run/session capture events.
• Resolve merge with upstream main.

Validation:

• Ran extension build successfully with no errors.
• Manually verified CodeChat Editor loads in Extension Development Host.
• Manually verified session_start appears in CodeChat Capture output.