Add rendering cleanup plan for texture management and code simplification

docs/planning/rendering-cleanup-plan.md

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+# Rendering Cleanup Plan - Texture Management and Code Simplification
+
+## Objective
+Clean up rendering code by removing unused spacecraft texture system, consolidating texture loading to initialization, and simplifying other rendering functions.
+
+## Background
+The renderer has several inefficiencies:
+- `ensure_textures_loaded()` called every frame instead of once during initialization
+- Spacecraft texture system now redundant with `render_child_indicators()` providing visibility
+- Unused `render_body()` function with FIXME comment
+- Hardcoded constants scattered throughout rendering code
+- Documentation inconsistency between RenderState and UIState
+
+## Implementation
+
+### Step 1: Save Plan (Current)
+- Create this plan document in docs/planning/
+- **PAUSE** for user review
+
+### Step 2: Move Texture Loading to Initialization
+- Modify `init_renderer()` or `setup_camera()` to call `ensure_textures_loaded()` once
+- Remove `ensure_textures_loaded()` calls from:
+  - `render_spacecraft_screen_space()` (renderer.cpp:385)
+  - `render_maneuver_marker_screen_space()` (renderer.cpp:420)
+- Update docs/technical_reference.md if it references texture loading behavior
+- **PAUSE** for user review
+
+### Step 3: Remove Spacecraft Texture System
+Remove all spacecraft texture-related code:
+- From RenderState struct (renderer.h:19): `Texture2D spacecraft_texture;`
+- From renderer.cpp:
+  - `generate_spacecraft_texture()` function (lines 112-124)
+  - `calculate_spacecraft_angle()` function (lines 156-164)
+  - `render_spacecraft_screen_space()` function (lines 373-402)
+  - Texture initialization in `setup_camera()` (line 178)
+  - Texture unloading in `close_renderer()` (line 103)
+- Remove spacecraft rendering from main loop in `render_simulation()` (lines 694-697)
+- Remove from renderer.h:
+  - Function declaration for `generate_spacecraft_texture()` (line 29)
+  - Function declaration for `calculate_spacecraft_angle()` (line 36)
+  - Function declaration for `render_spacecraft_screen_space()` (line 45)
+- Update docs/rendering.md to remove spacecraft texture references
+- **PAUSE** for user review
+
+### Step 4: Remove Unused `render_body()` Function
+- Remove `render_body()` function from renderer.cpp (lines 359-371)
+- Remove function declaration from renderer.h (line 44)
+- Remove FIXME comment on line 357
+- Update docs/rendering.md line 315 (references to render_body)
+- Update docs/technical_reference.md line 531 (references to render_body)
+- **PAUSE** for user review
+
+### Step 5: Simplify Maneuver Texture Selection
+- Replace switch statement (renderer.cpp:426-449) with direct array indexing
+- Since BurnDirection enum values are sequential (0-5), use `maneuver->direction` directly as texture_index
+- Handle BURN_CUSTOM case separately if needed
+- **PAUSE** for user review
+
+### Step 6: Extract UI Panel Constants
+- Add constants to ui_renderer.cpp:
+  - `INFO_PANEL_WIDTH = 300`
+  - `INFO_PANEL_HEIGHT = 300`
+  - `BODY_LIST_WIDTH = 200`
+  - `BODY_LIST_HEIGHT = 400`
+  - `BODY_INFO_WIDTH = 250`
+  - `BODY_INFO_HEIGHT = 300`
+  - `MANEUVER_LIST_WIDTH = 300`
+  - `MANEUVER_LIST_HEIGHT = 400`
+  - `MANEUVER_LIST_Y_OFFSET = 320`
+- Replace magic numbers in all UI rendering functions
+- **PAUSE** for user review
+
+### Step 7: Extract Child Indicator Constants
+- Add constants to renderer.cpp:
+  - `CHILD_INDICATOR_RADIUS = 20.0f`
+  - `CHILD_INDICATOR_FONT_SIZE = 10`
+- Replace magic numbers in `draw_child_indicator()` function
+- **PAUSE** for user review
+
+### Step 8: Fix Documentation Inconsistency
+- Update docs/rendering.md line 16 to reflect that `selected_craft_index` is in UIState, not RenderState
+- Update any other documentation that references this field location
+- **PAUSE** for user review
+
+### Step 9: Final Testing
+- Build project: `make`
+- Run simulation: `make run`
+- Verify spacecraft still visible via child indicators
+- Verify maneuver markers still render correctly
+- Verify UI panels still display correctly
+- Check for any texture-related warnings or errors
+- **PAUSE** for user review
+
+## Testing Plan
+- Build succeeds without errors
+- Spacecraft visible in child indicators when parent body selected
+- Maneuver markers display with correct colors and sizes
+- UI panels render with correct dimensions
+- No memory leaks from texture cleanup
+- Performance improvement (fewer function calls per frame)
+
+## References
+- docs/rendering.md - Rendering system documentation
+- docs/technical_reference.md - Technical reference
+- src/renderer.cpp/h - Main rendering code
+- src/ui_renderer.cpp/h - UI rendering code
+- AGENTS.md - Coding rules (no comments, C-style)
+
+## Date
+Created: 2026-01-30