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.

crates/audio/src/vad.rs

@@ -7,7 +7,7 @@
 // For now, all audio is treated as speech. This matches v0.2 behaviour
 // (no VAD) and doesn't affect core functionality.
 
-use kon_core::constants::VAD_SPEECH_THRESHOLD;
+use magnotia_core::constants::VAD_SPEECH_THRESHOLD;
 
 /// Stub speech detector. Treats all audio as speech.
 #[derive(Default)]