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.

src/game/enemy.h

@@ -44,4 +44,52 @@ typedef struct FlyerData {
 void flyer_register(EntityManager *em);
 Entity *flyer_spawn(EntityManager *em, Vec2 pos);
 
+/* ── Charger enemy ─────────────────────────────────── */
+/* Ground patrol that detects the player, telegraphs     */
+/* briefly, then charges at high speed. Stuns on wall.   */
+
+#define CHARGER_WIDTH   14
+#define CHARGER_HEIGHT  16
+#define CHARGER_PATROL_SPEED  30.0f  /* slow patrol (px/s)        */
+#define CHARGER_CHARGE_SPEED  150.0f /* charge rush speed (px/s)  */
+#define CHARGER_DETECT_RANGE  200.0f /* horizontal detect (px)    */
+#define CHARGER_CHARGE_TIME   2.0f  /* max charge duration (s)   */
+#define CHARGER_HEALTH  2
+
+typedef enum ChargerState {
+    CHARGER_PATROL,
+    CHARGER_ALERT,      /* telegraph before charging            */
+    CHARGER_CHARGE,     /* full-speed horizontal rush           */
+    CHARGER_STUNNED,    /* hit a wall, briefly vulnerable       */
+} ChargerState;
+
+typedef struct ChargerData {
+    ChargerState state;
+    float        patrol_dir;     /* 1.0 or -1.0                  */
+    float        state_timer;    /* countdown for current state   */
+    float        death_timer;
+} ChargerData;
+
+void    charger_register(EntityManager *em);
+Entity *charger_spawn(EntityManager *em, Vec2 pos);
+
+/* ── Spawner enemy ─────────────────────────────────── */
+/* Stationary, periodically spawns grunt enemies up to   */
+/* a cap. Destructible.                                  */
+
+#define SPAWNER_WIDTH   16
+#define SPAWNER_HEIGHT  16
+#define SPAWNER_HEALTH  3
+#define SPAWNER_INTERVAL 4.5f   /* seconds between spawns        */
+#define SPAWNER_MAX_ALIVE 3     /* max grunts alive at once       */
+
+typedef struct SpawnerData {
+    float spawn_timer;           /* countdown to next spawn       */
+    float death_timer;
+    float pulse_timer;           /* visual pulse before spawn     */
+} SpawnerData;
+
+void    spawner_register(EntityManager *em);
+Entity *spawner_spawn(EntityManager *em, Vec2 pos);
+
 #endif /* JNR_ENEMY_H */