Usability & Ergonomics Improvements

All issues identified across Sections 3.1, 3.2, and 3.3 have been
resolved, verified with unit tests, automated compilation checks under
`-D float_literal_f32_fallback`, and headless SVG export runs.

-
  **[angle.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/src/general/angle.rs)**:
  - Implemented `From<f64>` and `From<usize>` for `Degrees`.
  - Added unit tests `from_integer` and `from_f64` to verify conversion
    accuracy.
-
  **[fontsize.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/src/general/fontsize.rs)**:
  - Implemented `From<f64>` for `FontSize`.
  - Refactored `FontSize::value(self)` to pass Copy type by value.
  - Added unit test `font_size_conversions`.
-
  **[general.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/src/general.rs)**:
  - Implemented `From<f64>`, `From<i32>`, and `From<usize>` for
    `AnimationSpeed`.
  - Added unit test `animation_speed_conversions`.
  - Re-exported `macroquad` crate (`pub use macroquad;`) so downstream
    code and macro expansions have reliable direct access.

-
  **[export.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/src/export.rs)**:
  - Made `parse_svg_export_arg()` public.
  - Implemented `run_headless_svg_export<F>(mut build_commands: F,
    filename: &str) -> Result<(), ExportError>` that executes commands
    using `app.step_animations()`, avoiding all window/GUI dependencies
    and never calling `std::process::exit`.
  - Updated `handle_svg_export` to delegate to
    `run_headless_svg_export`.
-
  **[lib.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/src/lib.rs)**:
  - Extracted `pub fn step_animations(&mut self)` from `update(&mut
    self)`, allowing command queue draining and tween stepping
    headlessly without querying window mouse position or events.
-
  **[state.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/src/state.rs)**:
  - Changed `TurtleWorld::new()` to initialize camera with
    `Camera2D::default()` instead of querying `screen_width()` /
    `screen_height()`, eliminating panics when running without a
    Macroquad window.
-
  **[turtle-lib-macros/src/lib.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib-macros/src/lib.rs)**:
  - Added `validate_input` helper providing clean compile diagnostics
    with spans for:
    - Multiple arguments: `#[turtle_main] functions must take either 0
      arguments or a single &mut TurtlePlan`
    - Non-unit return types: `#[turtle_main] functions cannot have a
      return type`
    - Async functions: `#[turtle_main] functions cannot be async`
  - Replaced `#[macroquad::main]` wrapper expansion with a native `fn
    main()` that inspects CLI arguments first. If `--export-svg` is
    present, it runs `run_headless_svg_export` directly and returns
    cleanly without opening a window. Otherwise, it launches
    `macroquad::Window::new(#window_title, async { ... })`.
  - Added 5 unit tests in `turtle-lib-macros` testing signature
    validation.

-
  **[.vscode/launch.json](file:///home/dietrich/Projekte/Source/turtlers/.vscode/launch.json)**:
  - Removed stale references to nonexistent `turtle-example` and
    `turtle-ui`.
  - Added debug configurations for `turtle-lib` tests,
    `turtle-lib-macros` tests, `hello_turtle`, and `breadboard`.
-
  **[breadboard.rs](file:///home/dietrich/Projekte/Source/turtlers/turtle-lib/examples/breadboard.rs)**:
  - Refactored example to use `#[turtle_main("Breadboard")]`.
  - Removed `#[cfg(feature = "svg")]` and the early-exit message; the
    example now renders directly on screen by default and supports
    `--features svg -- --export-svg breadboard.svg`.
-
  **[README.md](file:///home/dietrich/Projekte/Source/turtlers/README.md)**:
  - Documented optional user-level `~/.cargo/config.toml` mold/lld
    fast-linking configuration under "Building and Running".

---

```bash
cargo test --workspace
```
- **Result**: 21 passed (16 in `turtle-lib`, 5 in `turtle-lib-macros`),
  34 doctests passed, 0 failed.

```bash
RUSTFLAGS="-D float_literal_f32_fallback" cargo check --workspace
--all-targets --all-features
RUSTFLAGS="-D float_literal_f32_fallback" cargo check --package
turtle-lib --examples --all-features
```
- **Result**: Passed with 0 errors and 0 fallback warnings across all
  workspace crates and all 30 examples.

```bash
cargo run --package turtle-lib --example hello_turtle --features svg --
--export-svg hello.svg
cargo run --package turtle-lib --example breadboard --features svg --
--export-svg breadboard.svg
```
- **Result**: Both exported SVG files successfully and exited with code
  0 without creating or flashing a graphical window.

```bash
cargo check --package turtle-lib --example breadboard
```
- **Result**: Compiled cleanly with 0 errors when SVG feature is
  disabled.

turtle-lib/src/lib.rs

@@ -73,6 +73,9 @@ pub(crate) mod export_svg;
 // Re-export the turtle_main macro
 pub use turtle_lib_macros::turtle_main;
 
+// Re-export the macroquad crate so generated macro code can access it directly
+pub use macroquad;
+
 // Re-export common macroquad types and colors for convenience
 pub use macroquad::prelude::{
     vec2, BLACK, BLUE, DARKGRAY, GOLD, GREEN, ORANGE, PURPLE, RED, WHITE, YELLOW,
@@ -282,12 +285,19 @@ impl TurtleApp {
         }
     }
 
-    /// Update animation state (call every frame)
+    /// Update animation state and process window mouse events (call every frame in GUI loop)
     pub fn update(&mut self) {
         // Handle mouse panning and zoom
         self.handle_mouse_panning();
         self.handle_mouse_zoom();
 
+        self.step_animations();
+    }
+
+    /// Drive animation updates for all turtles without querying window or mouse events.
+    ///
+    /// Suitable for headless execution (such as CLI SVG export) where no graphics window exists.
+    pub fn step_animations(&mut self) {
         // Update all turtles' tween controllers
         for turtle in &mut self.world.turtles {
             // Drive this turtle's animation controller for one frame.