2.9.6 — Fix Power never registering as on (UHD60)

Fixed

• Power switch permanently stuck reading `off` even while the UHD60 stayed on, confirmed via debug logs showing `RX <- Optoma_PJ> OK1` on every single poll — unstripped, despite v2.9.5's fix. Root cause: that fix anchored its strip to the very start of the line, but the power read's raw reply had stray control/escape bytes or an embedded line break in front of the prompt that plain `.strip()` doesn't remove, so the anchored match never fired.
• Replaced prefix-stripping with marker search: instead of assuming the console noise is a clean, strippable prefix, search the line for a real protocol marker (`Ok`, `INFOn`, or a bare `P`/`F` at the end) and keep only from there on — regardless of what precedes it or how it's shaped. This also subsumes the single-echo and doubled-echo cases from v2.9.1/v2.9.5 in one pass.

This should be the last variant of the console-noise problem — the new approach doesn't rely on the noise having any particular shape, just that a real reply marker exists somewhere in the line.