fix(extension): stabilize update marker

[iFwu]

Description

Use the timestamp embedded in the upstream README config block for the generated explorer.fileNesting.patterns["//"] marker instead of formatting the local update time with toLocaleString().

Before this change, the extension rewrote the marker with each machine's local locale, for example:

"//": "Last update at 2026/4/23 22:05:30"
"//": "Last update at 4/27/2026, 4:01:10 PM"

When VS Code/Cursor settings are synced across Windows and macOS (via Settings Sync, dotfiles, or a git-tracked settings.json), the same upstream file-nesting config can therefore create platform-specific churn and merge conflicts even when the actual nesting patterns are identical.

This keeps the previous marker shape (Last update at ...) but makes the value deterministic by reusing the upstream README timestamp, for example:

"//": "Last update at 2026-04-20 00:47 UTC"

The marker is not used for file-nesting parsing or config comparison: the extension already removes the "//" marker before comparing local patterns, while the upstream README parser strips JSONC comment lines before JSON.parse.

Linked Issues

N/A. No exact existing issue/PR was found for the locale-specific update marker; related updater behavior discussions include #127 and #218.

Verification

• git diff --check
• Parsed the current README config block with Node to verify the upstream timestamp and JSON extraction still work.