integrate zat SDK, fix quoted phrase search
- add zat dependency for ATProto primitives
- replace hand-rolled Did/AtUri with zat.Did.parse
- use zat.json.extractAt for type-safe JSON parsing in tap.zig
- fix quoted phrase search (pass through to FTS5 unchanged)
- redirect zig-patterns.md to notes repo
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>