D1: Normalize VS Code status values (completed → success)

[Arithmomaniac]

Parent: #54

Problem

VS Code produces completed/pending status; CLI produces success/error/None. While the CSS already treats success and completed identically, the semantic inconsistency means status badges show different labels for the same outcome.

Change

In _parse_tool_invocation_serialized() (line 101 of scanner/vscode.py):

• Map completed → success
• Detect error conditions where possible (isComplete=false with error indicators) → error
• Keep pending for incomplete items

Scope

~3 lines in src/copilot_session_tools/scanner/vscode.py

Conflict note

Different lines from agent-collapsibles branch changes (their additions are at lines 113-122). Safe.