Add L16 integration tests, update docs and wrangler.toml for CF deployment
New test/integration.test.ts with 6 end-to-end tests:
- Full lifecycle: signup → write → read → CAR export → firehose events
- Multi-agent isolation: two agents on separate Account DOs
- DID lifecycle: signup creates did:plc, resolveHandle returns it
- Enrollment edge cases: duplicate handle, duplicate thumbprint, auth failures
- Blob round-trip: uploadBlob → getBlob via HTTP routes
- Lexicon-agnostic: various collection NSIDs accepted
Updated README.md: CF Worker architecture, wrangler quickstart, binding tables.
Updated docs/agent-guide.md: removed Node.js prerequisite.
Updated wrangler.toml: added [vars] for pds.solpbc.org.
Deleted schema/directory.sql (initDirectory() is authoritative).