drift

Added

• boids scene — Reynolds flocking simulation; triangle-arrow heads with fading trails, three steering rules (separation, alignment, cohesion); configurable count and speed
• plasma scene — classic demoscene sine-sum color field; four overlapping waves with a drifting radial center; density characters (░▒▓█) layer depth; configurable speed and scale
• engine.oled_shift config flag (default false) — OLED pixel-shift now opt-in instead of always active

Changed

• dvd base speed raised from 10 → 16 cells/s (vy 5 → 8); crosses a new cell boundary roughly every 2 frames at 30 fps for noticeably smoother motion; tune back with speed = 0.65

Fixed

• dvd bounce now reflects the overshoot (2·maxX − x) instead of clamping to the wall; eliminates the one-frame "stick" before reversing direction
• dvd double velocity-flip on tiny terminals: when the logo is wider/taller than the available space, velocity is zeroed instead of being flipped twice (which left the logo oscillating in place)
• plasma spatial frequency doubled (base multiplier 6 → 12); blobs are now small enough relative to the terminal that edges cut through the middle of a pattern instead of at a band boundary
• Scene name matching is now case-insensitive (--scene Rain works, not just --scene rain)
• Unknown scene names in --scene / config now print a warning to stderr instead of silently falling back to all scenes