fix(copy): replace em-dashes in user-facing strings with commas/periods

Per the project's no-dashes feedback rule (see CORBEL-Main memory
feedback_no_dashes.md), em-dashes in user-visible copy are the single
biggest "AI wrote this" surface tell. Forty-two occurrences across ten
files: ten in SettingsPage's group descriptions and option labels
(audio device picker, vocabulary help, prompt placeholders, model
descriptions), four in FirstRunPage's setup steps, three in
DictationPage / FilesPage / Energy chip tooltips, plus the privacy
bullets ("100% offline, no Python required, no cloud, no accounts,
no telemetry"), the rejection toast, MicroSteps thumb labels, and the
shutdown ritual prompts.

Replacement rule: subordinate-clause em-dashes followed by lowercase
become commas; sentence-break em-dashes followed by capitals become
full stops. Code comments left intact.

One non-em-dash regression caught while reviewing: TasksPage's energy
filter "no selection" placeholder showed "—" as a literal label; the
script changed it to a comma which read as a UI bug. Replaced with
"Any" instead.

src/lib/pages/FirstRunPage.svelte

@@ -227,7 +227,7 @@
       <Play size={32} strokeWidth={1.5} class="text-accent mx-auto mb-3" />
       <h2 class="text-xl font-medium text-text">Launch Magnotia at login?</h2>
       <p class="text-sm text-text-secondary mt-3 leading-relaxed">
-        So Magnotia is already there when you need it — especially useful if you said yes to morning triage. Uses your OS's standard autostart. No background tricks, no telemetry.
+        So Magnotia is already there when you need it, especially useful if you said yes to morning triage. Uses your OS's standard autostart. No background tricks, no telemetry.
       </p>
       <p class="text-[11px] text-text-tertiary mt-3">You can change this any time in Settings.</p>
       <div class="flex items-center justify-center gap-3 mt-6">
@@ -264,7 +264,7 @@
       </div>
       <p class="text-xs text-text-tertiary mt-2">{downloadProgress}%</p>
       {#if estimatedMinutes > 2}
-        <p class="text-xs text-text-secondary mt-3">Download in background — this may take a while</p>
+        <p class="text-xs text-text-secondary mt-3">Download in background, this may take a while</p>
       {/if}
     </div>
 
@@ -296,7 +296,7 @@
       {#if models.length > 0}
         <div class="mt-6">
           <h3 class="text-xs font-medium text-text-tertiary uppercase tracking-wider mb-3">Pick a model</h3>
-          <p class="text-xs text-text-tertiary mb-3">One tap — we handle the rest.</p>
+          <p class="text-xs text-text-tertiary mb-3">One tap, we handle the rest.</p>
           <div class="space-y-2">
             {#each models as model, i}
               <button
@@ -330,7 +330,7 @@
         style="transition-duration: var(--duration-ui)"
         onclick={skipSetup}
       >
-        Skip setup — I'll configure later
+        Skip setup. I'll configure later
       </button>
     </div>
   {/if}