F-38: Hot-path logging and repaint cost #41

Severity: LOW · Effort: Small · Batch: 5 · Status: Code done in #21 (29b54d2), awaiting bench verification

Found in the second full review of the firmware. Recorded with the rest of the pass (F-19…F-44) in docs/REVIEW_REMEDIATION_PLAN_2.md, which is where its status is kept.

• Every received WiThrottle line, knob tick and throttle update logs at INFO; console writes
  block the encoder and receive tasks.
• PowerStatusBar::refresh() runs four times per repaint, and labels are rewritten (and so
  invalidated) even when unchanged.

Acceptance Criteria

• Per-line, per-tick and per-update logs are DEBUG: WiThrottle RX, direction commands,
  the controller's knob and update lines, the virtual encoder.
• PowerStatusBar::refresh() runs once per repaint, and it and the knob indicators skip
  any widget whose look has not changed. (ThrottleMeter already did for its labels.)
• Bench: spin a knob hard with the console attached; the display keeps up.