Implements record deletion with proper ATProto event emission:
- Removes record from database and rebuilds MST
- Creates signed commit with updated repo state
- Emits delete event to firehose for relay/indexer propagation
- Routes POST requests with repo in body to correct Durable Object

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ATProto MST spec: "Layers are counted from the bottom of the tree,
starting with zero." This means:
- Layer 0 is at the BOTTOM
- Root is at the HIGHEST layer (max depth of any key)
- Subtrees go DOWN to lower layers

Previous implementation had this inverted, causing "depths are out of
order" validation errors in pdsls.

Also includes:
- MST nodes must include l and t fields (even when null) per ATProto schema
- handleGetRepo now only includes blocks reachable from current commit

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

- Add scripts/update-did.js for updating PLC DID handle and PDS endpoint
- Fix handle resolution to work with bare domain handles (not just subdomains)
- This allows workers.dev deployments where nested subdomains aren't supported

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>