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.

package.json

@@ -1,7 +1,7 @@
 {
-  "name": "kon",
+  "name": "magnotia",
   "version": "0.1.0",
-  "description": "Kon — Think out loud",
+  "description": "Magnotia — Think out loud",
   "type": "module",
   "scripts": {
     "dev": "npm run dev:frontend",