chore: rebrand from Kon/Corbie to Magnotia

Replace all instances of the legacy product names "Kon" and "Corbie" with
"Magnotia" across user-facing copy, code identifiers, package names, bundle
ids, file paths, and documentation. Preserves the unrelated "konsole" (KDE
terminal) reference and the parent CORBEL company name.

- Renames 10 Rust crates (kon-* → magnotia-*) and the tauri binary
- Updates package.json, tauri.conf.json (productName + identifier)
- Renames CSS classes (kon-rh-* → magnotia-rh-*) and animations
- Renames brand and roadmap docs
- Regenerates Cargo.lock and package-lock.json

Verified: svelte-check passes; pure-rust crates compile under new names.

src-tauri/src/commands/fs.rs

@@ -35,7 +35,7 @@ mod tests {
     #[tokio::test]
     async fn write_text_file_errors_on_bad_parent() {
         let result = write_text_file_cmd(
-            "/definitely-not-a-real-path-kon-phase9/out.md".into(),
+            "/definitely-not-a-real-path-magnotia-phase9/out.md".into(),
             "x".into(),
         )
         .await;