Implement four feature phases:
Phase 1 - Pause menu: extract bitmap font into shared engine/font
module, add MODE_PAUSED with Resume/Restart/Quit overlay.
Phase 2 - Laser turret hazard: ENT_LASER_TURRET with charge/fire/
cooldown state machine, per-pixel beam raycast, two variants (fixed
and tracking). Registered in entity registry with editor icons.
Phase 3 - Charger and Spawner enemies: charger ground patrol with
detect/telegraph/charge/stun cycle (2s charge timeout), spawner that
periodically creates grunts up to a global cap of 3.
Phase 4 - Mars campaign: two handcrafted levels (mars01 surface,
mars02 base), mars_tileset.png, PARALLAX_STYLE_MARS with salmon sky
and red mesas, THEME_MARS_SURFACE/THEME_MARS_BASE for the procedural
generator with per-theme gravity/tileset/parallax. Moon campaign now
chains moon03 -> mars01 -> mars02 -> victory.
Also fix review findings: deterministic seed on generated level
restart, NULL checks on calloc in spawn functions, charge timeout
to prevent infinite charge on flat terrain, and stop suppressing
stderr in Makefile web-serve target so real errors are visible.
WIND directive in .lvl files sets a constant horizontal force (px/s^2)
that pushes entities, projectiles, and particles. Positive is rightward.
Wind is applied as acceleration in physics_update() (halved on ground),
directly to projectile and particle velocities, and as a gentle position
drift on flyers. Entities with gravity_scale=0 (drones, spacecraft) are
unaffected. Levels default to no wind when the directive is absent.
