v0.2.0: docs: runnable debug builds, bit-sync bench, and the bit-sync finding

Note in AGENTS that iteration can drop --release (the dev profile makes debug
builds runnable), document examples/bitsync_bench.rs, and record the slow
bit-sync investigation under open issues: the bit-sync logic is sound (clean
synth holds sync), the SJTU/HackRF failure is degraded prompt-I plus a brittle
recovery path that hard-resets on one failed frame-sync check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>