feat: add shared Rust crates for cross-platform time utilities

Introduce `bridge` proc-macro crate with `#[export]` attribute that conditionally applies `wasm_bindgen` for WASM builds, and `time` crate porting all timecode/frame utilities from TypeScript to Rust.

rust/crates/bridge/src/bridge.rs

@@ -0,0 +1,49 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{ItemFn, parse_macro_input};
+
+#[proc_macro_attribute]
+pub fn export(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let function = parse_macro_input!(item as ItemFn);
+    let js_name = snake_to_camel(&function.sig.ident.to_string());
+
+    quote! {
+        #[cfg_attr(feature = "wasm", ::wasm_bindgen::prelude::wasm_bindgen(js_name = #js_name))]
+        #function
+    }
+    .into()
+}
+
+fn snake_to_camel(name: &str) -> String {
+    let mut camel = String::with_capacity(name.len());
+    let mut should_uppercase_next = false;
+
+    for character in name.chars() {
+        if character == '_' {
+            should_uppercase_next = true;
+            continue;
+        }
+
+        if should_uppercase_next {
+            camel.push(character.to_ascii_uppercase());
+            should_uppercase_next = false;
+            continue;
+        }
+
+        camel.push(character);
+    }
+
+    camel
+}
+
+#[cfg(test)]
+mod tests {
+    use super::snake_to_camel;
+
+    #[test]
+    fn converts_snake_case_to_camel_case() {
+        assert_eq!(snake_to_camel("do_something"), "doSomething");
+        assert_eq!(snake_to_camel("a_b_c"), "aBC");
+        assert_eq!(snake_to_camel("already"), "already");
+    }
+}