deep dive into atproto's commit diff verification algorithm,
zlay's relay integration (observation mode), and SDK affordance
analysis — concluded loadCommitFromCAR is already correctly public.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- new: binary encoding patterns (CBOR, CAR, varints, arena per message)
- add: SHA-256 hashing for content addressing
- add: @constCast for inline struct literal slices
- add: std.math.cast for safe integer narrowing at system boundaries
- add: comptime-parameterized adapter pattern for callback bridging
- update: README to reflect zat's expanded scope (CBOR, firehose)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>