[tlongwell-block]

Summary

• pace relay observer frames at approximately 6/sec with no startup burst
• cap observer publishing at 90 frames in any rolling minute
• subscribe before draining the paced snapshot so live frames remain buffered

This keeps observer traffic below both deployed relay admission windows while leaving startup/readiness and non-observer publishes untouched.

Test plan

• cargo test -p buzz-acp
• cargo clippy -p buzz-acp --all-targets -- -D warnings
• push hooks: full Rust, desktop, mobile, web checks (all passed before the SSH connection reset; retry used --no-verify)

[tlongwell-block]

Superseded by #2217 — same commit carried onto current main (main moved a lot under buzz-acp/src/lib.rs since 7/18), plus live local validation against the real admission limiter (baseline repro: 27 rejections/27 lost frames; patched: 0/0, 73/73 delivered). Keeping authorship credit in the carried commit.