Update rendering.md: UIState and ManeuverDialogState documentation

docs/rendering.md

@@ -26,6 +26,37 @@ struct UIState {
     int body_list_scroll;         // Scroll position for body list
     int body_list_active;         // Active item index in body list
     int selected_craft_index;     // Selected spacecraft index (-1 = no selection)
+
+    int maneuver_list_active;
+    int maneuver_list_scroll;
+    int selected_maneuver_index;
+
+    int cached_body_count, cached_craft_count;
+    int cached_maneuver_count, cached_executed_count;
+    char* body_list_buffer; int body_list_buffer_size;
+    char* craft_list_buffer; int craft_list_buffer_size;
+    char* body_dropdown_buffer; int body_dropdown_buffer_size;
+    char* maneuver_list_buffer; int maneuver_list_buffer_size;
+
+    ManeuverDialogState maneuver_dialog;
+};
+```
+
+### ManeuverDialogState (ui_renderer.h)
+```cpp
+struct ManeuverDialogState {
+    bool open;
+    ManeuverDialogTab active_tab;
+    int craft_index, direction_active;
+    double delta_v, trigger_value;
+    int edit_maneuver_index;
+    int target_body_index, current_body_index, transfer_body_index;
+    bool show_hohmann_preview;
+    HohmannTransfer last_calc;
+    bool show_preview, preview_valid;
+    OrbitalElements preview_elements;
+    char error_message[256];
+    bool show_error, show_delete_confirm;
 };
 ```
 
@@ -282,6 +313,8 @@ When a spacecraft is selected:
 **Dimensions:** 300×400 pixels
 **Position:** Y=320 (below info panel)
 
+Dropdown lists use cached buffers, rebuilt only when object counts change.
+
 ## Rendering Pipeline
 
 ### Main Loop Sequence
@@ -354,9 +387,8 @@ Note: UI rendering functions are called after `render_simulation()` to ensure UI
 - Helps orient user in 3D space
 
 ### Memory Management
-- UI panels allocate temporary buffers for lists
+UI buffers persist between frames and rebuild when object counts change.
-- List text freed after rendering
+Buffers freed on shutdown via ui_state_free_buffers().
-- No persistent UI state allocation
 
 ## TODO Items