chore: address rustfmt + CodeRabbit review debt from PR #750 admin-merge

[zackees]

Sub-issue of #755 (post-#750 follow-up meta).

What

PR #750 was admin-merged with two CI failures bypassed:

1. Formatting (rustfmt) — the new task bodies in crates/fbuild-daemon/src/handlers/websockets.rs weren't cargo-fmt'd. Diff sample from the CI log:

   // What I wrote:
   let _ = out_tx_inbound.send(SerialServerMessage::WriteAck {
       success: false,
       bytes_written: 0,
       message: Some(format!("write error: {}", e)),
   });
   
   // What rustfmt wants:
   let _ = out_tx_inbound
       .send(SerialServerMessage::WriteAck {
           success: false,
           bytes_written: 0,
           message: Some(format!("write error: {}", e)),
       });

2. CodeRabbit review — was still in PENDING state at merge time. Any review comments that landed after the merge are unaddressed.

Acceptance

• soldr cargo fmt --check is clean on crates/fbuild-daemon/src/handlers/websockets.rs against master.
• All CodeRabbit comments on PR perf(serial): split daemon WS handler into reader/writer/inbound (closes #749) #750 are either addressed in a follow-up commit or explicitly closed with rationale.

Why this is a separate sub-issue

These are housekeeping, not behavior changes. Worth a focused 1-2-commit PR so the diff is easy to review and the new green-CI baseline is established before the heavier #756 / #757 work lands on top.

Cross-links

• Meta: [meta] Post-#750 follow-ups: Fix Fbuild ClearBuffer/GetInWaiting, the fix auto research, tests, review-debt #755
• Original merged PR: perf(serial): split daemon WS handler into reader/writer/inbound (closes #749) #750

[zackees]

Closing — both acceptance criteria verified met against current main:

1. ✅ soldr cargo fmt -p fbuild-daemon --check is clean on crates/fbuild-daemon/src/handlers/websockets.rs (verified on main at 7566337). The format drift from the perf(serial): split daemon WS handler into reader/writer/inbound (closes #749) #750 admin-merge was picked up by upstream PR fix(ci): cargo fmt + split 4 .rs files under 1000 LOC #752 ("cargo fmt + split 4 .rs files under 1000 LOC").

2. ✅ CodeRabbit comments on PR perf(serial): split daemon WS handler into reader/writer/inbound (closes #749) #750 — gh api repos/FastLED/fbuild/pulls/750/comments returns [], i.e. zero actionable inline comments. Only the high-level auto-summary was posted (description check / title check / linked-issues check — all ✅ Passed). Nothing to address.

The "review debt" framing turned out to be precautionary; no actual debt accrued. Closing as part of meta #755 wrap-up.