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/lib/Sidebar.svelte

@@ -47,17 +47,17 @@
   <div class="flex items-center {collapsed ? 'justify-center px-0 pt-4 pb-1' : 'px-5 pt-4 pb-1'} relative">
     {#if !collapsed}
       <div class="flex items-center gap-2 flex-1 min-w-0">
-        <h1 class="font-display text-[26px] text-text tracking-tight leading-none italic">Kon</h1>
+        <h1 class="font-display text-[26px] text-text tracking-tight leading-none italic">Magnotia</h1>
         <span
           class="text-[18px] text-accent inline-block {page.recording ? 'animate-sinhala-spin' : ''}"
-          title="Kon"
+          title="Magnotia"
         >&#3559;</span>
       </div>
     {:else}
       <!-- Collapsed: just the decorative character centred -->
       <span
         class="text-[18px] text-accent inline-block {page.recording ? 'animate-sinhala-spin' : ''}"
-        title="Kon"
+        title="Magnotia"
       >&#3559;</span>
     {/if}
   </div>