Add updatedAt-based conflict resolution for pinnedExtensions

[JonahBraun]

When both local and remote modify the same pin entry during a merge, use the updatedAt timestamp to determine the winner — the most recent change takes precedence. Stable (unpin) entries default to updatedAt: 0 so any active pin always wins over an unpin unless the unpin is newer.

Part of the extension pinning project. See the architecture doc.

Changes

• Add updatedAt field to the PinnedExtension type in types/index.d.ts
• Add pin-specific conflict resolution in resolvers.ts that compares updatedAt timestamps when both sides modified the same pin entry

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Note

Medium Risk
Changes merge behavior for metadata.json extension pin entries, which could affect how sync conflicts are resolved and potentially override a user's intended pin/unpin if timestamps are wrong or missing.

Overview
Adds pin-specific conflict resolution for meta.pinnedExtensions during metadata.json 3-way merges: when both ours and theirs changed the same pin entry, the version with the highest updatedAt now wins.

Extends the project metadata type so each pinnedExtensions record includes updatedAt (and documents that version "stable" represents an unpinned state).

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