Add pause menu, laser turret, charger/spawner enemies, and Mars campaign

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.

Makefile

@@ -128,9 +128,9 @@ web-serve: web
 	@echo ""
 	@echo "Serving at http://localhost:$(WEB_PORT)/jnr.html"
 	@echo "Ctrl+C to stop."
-	@python3 -m http.server $(WEB_PORT) --directory dist-web 2>/dev/null || \
-	python  -m http.server $(WEB_PORT) --directory dist-web 2>/dev/null || \
-	echo "Python not found."
+	@python3 -m http.server $(WEB_PORT) --directory dist-web || \
+	python  -m http.server $(WEB_PORT) --directory dist-web || \
+	echo "Error: Python not found. Install python3 to serve."
 
 # ── Windows cross-compilation ───────────────────
 WIN_DIST := dist-win64