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/resources/windows/README.md

@@ -1,6 +1,6 @@
 # Windows bundle resources
 
-Files in this directory ship side-by-side with `kon.exe` to avoid the
+Files in this directory ship side-by-side with `magnotia.exe` to avoid the
 DLL-hell failure modes reported in Whispering #840 / #829 and Buzz
 #1459. They are **not** committed to the repo.