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/tauri.conf.json

@@ -1,8 +1,8 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
-  "productName": "Kon",
+  "productName": "Magnotia",
   "version": "0.1.0",
-  "identifier": "uk.co.corbel.kon",
+  "identifier": "uk.co.corbel.magnotia",
   "build": {
     "beforeDevCommand": "npm run dev:frontend",
     "devUrl": "http://localhost:1420",
@@ -12,7 +12,7 @@
   "app": {
     "windows": [
       {
-        "title": "Kon",
+        "title": "Magnotia",
         "width": 1020,
         "height": 720,
         "minWidth": 960,