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.

docs/brief/competitive-landscape.md

@@ -1,4 +1,4 @@
-<!-- Source: Kon Master Brief — §13 Competitive Landscape (Extended) -->
+<!-- Source: Magnotia Master Brief — §13 Competitive Landscape (Extended) -->
 
 ## 13. Competitive Landscape (Extended)
 
@@ -44,8 +44,8 @@
 - Tasks, habits, calendar, mood tracking, journalling with end-to-end encryption on desktop
 - Privacy-focused, small user base
 
-### Kon's advantages over the entire field
-| Kon | The field |
+### Magnotia's advantages over the entire field
+| Magnotia | The field |
 |---|---|
 | Cross-platform desktop + mobile (Tauri) | Almost all competitors are mobile-first or web-only |
 | Voice as primary input method | No mature competitor integrates voice into a full planning system |
@@ -59,4 +59,4 @@
 3. **Architecture:** Privacy-conscious and offline-first users served only by open-source tools and tiny startups.
 4. **Pricing:** Only Structured offers lifetime. Subscription fatigue is extreme in this demographic.
 
-Kon addresses all four simultaneously. No current competitor does.
+Magnotia addresses all four simultaneously. No current competitor does.