feat(cli): improve tmux theme detection with multiple query strategies

Enhances terminal theme detection in tmux environments by implementing
multiple OSC query strategies and environment variable fallbacks.

- Add tmuxPassthroughState() to detect tmux allow-passthrough setting -
Refactor buildOscQueries() to return array of query strategies - Try
passthrough-wrapped and unwrapped queries based on tmux config - Add
detectBgColorFromEnv() for TERM_BACKGROUND and COLORFGBG parsing - Add
xtermColorToRGB() helper for 256-color palette conversion - Add
XTERM_COLOR_STEPS and ANSI_16_COLORS lookup tables - Extract
sendOscQuery() for better query execution control - Set
OSC_QUERY_TIMEOUT_MS to 1000ms for reliable detection

Author: brandonkachen