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.

.github/workflows/check.yml

@@ -125,7 +125,7 @@ jobs:
         uses: Swatinem/rust-cache@v2
         with:
           workspaces: .
-          shared-key: kon-${{ matrix.os }}
+          shared-key: magnotia-${{ matrix.os }}
 
       - name: cargo check (workspace)
         run: cargo check --workspace --all-targets