Add in-game level editor with auto-discovered tile/entity palettes

Implements a full level editor that runs inside the game engine as an
alternative mode, accessible via --edit flag or E key during gameplay.
The editor auto-discovers available tiles from the tileset texture and
entities from a new central registry, so adding new game content
automatically appears in the editor without any editor-specific changes.

Editor features: tile painting (pencil/eraser/flood fill) across 3
layers, entity placement with drag-to-move, player spawn point tool,
camera pan/zoom, grid overlay, .lvl save/load, map resize, and test
play (P to play, ESC to return to editor).

Supporting changes:
- Entity registry centralizes spawn functions (replaces strcmp chain)
- Mouse input + raw keyboard access added to input system
- Camera zoom support for editor overview
- Zoom-aware rendering in tilemap, renderer, and sprite systems
- Powerup and drone sprites/animations wired up (were defined but unused)
- Bitmap font renderer for editor UI (4x6 pixel glyphs, no dependencies)

src/game/entity_registry.c

@@ -0,0 +1,108 @@
+#include "game/entity_registry.h"
+#include "game/player.h"
+#include "game/enemy.h"
+#include "game/projectile.h"
+#include "game/hazards.h"
+#include "game/powerup.h"
+#include "game/drone.h"
+#include <string.h>
+#include <stdio.h>
+
+EntityRegistry g_entity_registry = {0};
+
+/* ── Wrapper spawn functions ──────────────────────
+ * Some spawn functions need extra args beyond (em, pos).
+ * We wrap them to match the EntitySpawnFn signature.
+ * ──────────────────────────────────────────────────── */
+
+static Entity *spawn_platform_v(EntityManager *em, Vec2 pos) {
+    return mplat_spawn_dir(em, pos, vec2(0.0f, 1.0f));
+}
+
+static Entity *spawn_powerup_health(EntityManager *em, Vec2 pos) {
+    return powerup_spawn_health(em, pos);
+}
+
+static Entity *spawn_powerup_jetpack(EntityManager *em, Vec2 pos) {
+    return powerup_spawn_jetpack(em, pos);
+}
+
+static Entity *spawn_powerup_drone(EntityManager *em, Vec2 pos) {
+    return powerup_spawn_drone(em, pos);
+}
+
+/* ── Registry population ─────────────────────────── */
+
+static void reg_add(const char *name, const char *display,
+                    EntitySpawnFn fn, SDL_Color color, int w, int h) {
+    EntityRegistry *r = &g_entity_registry;
+    if (r->count >= MAX_REGISTRY_ENTRIES) return;
+    r->entries[r->count++] = (EntityRegEntry){
+        .name     = name,
+        .display  = display,
+        .spawn_fn = fn,
+        .color    = color,
+        .width    = w,
+        .height   = h,
+    };
+}
+
+void entity_registry_init(EntityManager *em) {
+    g_entity_registry.count = 0;
+
+    /* Register all entity behaviors with the entity manager */
+    player_register(em);
+    player_set_entity_manager(em);
+    grunt_register(em);
+    flyer_register(em);
+    projectile_register(em);
+    turret_register(em);
+    mplat_register(em);
+    flame_vent_register(em);
+    force_field_register(em);
+    powerup_register(em);
+    drone_register(em);
+
+    /* ════════════════════════════════════════════
+     *  REGISTRY TABLE
+     *
+     *  To add a new entity type to the game:
+     *  1. Create its .h/.c files
+     *  2. Register its behaviors above
+     *  3. Add one reg_add() line below
+     *
+     *  The editor will pick it up automatically.
+     * ════════════════════════════════════════════ */
+
+    /*        .lvl name       display name     spawn fn              color (editor)                w   h  */
+    reg_add("grunt",         "Grunt",          grunt_spawn,          (SDL_Color){200, 60, 60, 255},   GRUNT_WIDTH,   GRUNT_HEIGHT);
+    reg_add("flyer",         "Flyer",          flyer_spawn,          (SDL_Color){140, 80, 200, 255},  FLYER_WIDTH,   FLYER_HEIGHT);
+    reg_add("turret",        "Turret",         turret_spawn,         (SDL_Color){160, 160, 160, 255}, TURRET_WIDTH,  TURRET_HEIGHT);
+    reg_add("platform",      "Platform (H)",   mplat_spawn,          (SDL_Color){80, 180, 80, 255},   MPLAT_WIDTH,   MPLAT_HEIGHT);
+    reg_add("platform_v",    "Platform (V)",   spawn_platform_v,     (SDL_Color){80, 160, 100, 255},  MPLAT_WIDTH,   MPLAT_HEIGHT);
+    reg_add("flame_vent",    "Flame Vent",     flame_vent_spawn,     (SDL_Color){255, 120, 40, 255},  FLAME_WIDTH,   FLAME_HEIGHT);
+    reg_add("force_field",   "Force Field",    force_field_spawn,    (SDL_Color){60, 140, 255, 255},  FFIELD_WIDTH,  FFIELD_HEIGHT);
+    reg_add("powerup_hp",    "Health Pickup",  spawn_powerup_health, (SDL_Color){255, 80, 80, 255},   12, 12);
+    reg_add("powerup_jet",   "Jetpack Refill", spawn_powerup_jetpack,(SDL_Color){255, 200, 50, 255},  12, 12);
+    reg_add("powerup_drone", "Drone Pickup",   spawn_powerup_drone,  (SDL_Color){80, 200, 255, 255},  12, 12);
+
+    printf("Entity registry: %d types registered\n", g_entity_registry.count);
+}
+
+const EntityRegEntry *entity_registry_find(const char *name) {
+    for (int i = 0; i < g_entity_registry.count; i++) {
+        if (strcmp(g_entity_registry.entries[i].name, name) == 0) {
+            return &g_entity_registry.entries[i];
+        }
+    }
+    return NULL;
+}
+
+Entity *entity_registry_spawn(EntityManager *em, const char *name, Vec2 pos) {
+    const EntityRegEntry *entry = entity_registry_find(name);
+    if (!entry) {
+        fprintf(stderr, "entity_registry_spawn: unknown type '%s'\n", name);
+        return NULL;
+    }
+    return entry->spawn_fn(em, pos);
+}