Add per-level wind atmosphere property

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.

src/game/editor.c

@@ -450,6 +450,8 @@ static bool save_tilemap(const Tilemap *map, const char *path) {
 
     if (map->gravity > 0)
         fprintf(f, "GRAVITY %.0f\n", map->gravity);
+    if (map->wind != 0.0f)
+        fprintf(f, "WIND %.0f\n", map->wind);
     if (map->has_bg_color)
         fprintf(f, "BG_COLOR %d %d %d\n", map->bg_color.r, map->bg_color.g, map->bg_color.b);
     if (map->music_path[0])

src/game/enemy.c

@@ -170,6 +170,13 @@ static void flyer_update(Entity *self, float dt, const Tilemap *map) {
     float bob_offset = sinf(fd->bob_timer * FLYER_BOB_SPD) * FLYER_BOB_AMP;
     body->pos.y = fd->base_y + bob_offset;
 
+    /* Wind drifts flyers (they bypass physics_update).
+     * Apply as gentle position offset matching first-frame physics. */
+    float wind = physics_get_wind();
+    if (wind != 0.0f) {
+        body->pos.x += wind * dt * dt;
+    }
+
     /* Chase player if in range */
     Entity *player = find_player(s_flyer_em);
     if (player && player->active && !(player->flags & ENTITY_DEAD)) {

src/game/level.c

@@ -57,6 +57,9 @@ static bool level_setup(Level *level) {
         physics_set_gravity(DEFAULT_GRAVITY);
     }
 
+    /* Apply level wind (0 = no wind) */
+    physics_set_wind(level->map.wind);
+
     /* Apply level background color */
     if (level->map.has_bg_color) {
         renderer_set_clear_color(level->map.bg_color);

src/game/levelgen.c

@@ -1631,6 +1631,10 @@ bool levelgen_dump_lvl(const Tilemap *map, const char *path) {
         fprintf(f, "GRAVITY %.0f\n", map->gravity);
     }
 
+    if (map->wind != 0.0f) {
+        fprintf(f, "WIND %.0f\n", map->wind);
+    }
+
     if (map->has_bg_color) {
         fprintf(f, "BG_COLOR %d %d %d\n",
                 map->bg_color.r, map->bg_color.g, map->bg_color.b);

src/game/projectile.c

@@ -204,6 +204,12 @@ static void projectile_update(Entity *self, float dt, const Tilemap *map) {
         if (body->vel.y > MAX_FALL_SPEED) body->vel.y = MAX_FALL_SPEED;
     }
 
+    /* ── Apply wind ─────────────────────────── */
+    float wind = physics_get_wind();
+    if (wind != 0.0f) {
+        body->vel.x += wind * dt;
+    }
+
     /* ── Move ────────────────────────────────── */
     body->pos.x += body->vel.x * dt;
     body->pos.y += body->vel.y * dt;