fix(a11y): bump all text below 12px to 12px floor and promote tertiary-on-body to secondary

Brand guidelines (docs/brand/magnotia-brand-guidelines.md §4) say "Never go
below 12px for any text" and "tertiary text must be ≥18px bold or ≥24px
regular". Audit found 246 sub-12px className sites and 166 cases of
text-text-tertiary paired with body sizes.

Bumped text-[9/10/11px] → text-[12px] across 26 .svelte files in src/lib
and src/routes. Promoted text-text-tertiary → text-text-secondary at body
sizes (12-14px) where context allowed; left placeholder pseudo-states,
ternary-conditional inactive states, and line-through "done" states alone
(8 residual pairings, all decorative).

Affects neurodivergent users on 1366×768 budget hardware most directly.
svelte-check: 0 errors, 0 warnings.

src/lib/components/WipTaskList.svelte

@@ -60,7 +60,7 @@
 
   <!-- Active tasks (WIP-limited) -->
   {#if visibleTasks.length === 0}
-    <p class="text-[12px] text-text-tertiary text-center py-4">No active tasks</p>
+    <p class="text-[12px] text-text-secondary text-center py-4">No active tasks</p>
   {:else}
     <div class="flex flex-col gap-1">
       {#each visibleTasks as task (task.id)}
@@ -105,7 +105,7 @@
               {/if}
             </button>
             <button
-              class="text-text-tertiary hover:text-danger opacity-0 group-hover:opacity-100 text-[11px]"
+              class="text-text-secondary hover:text-danger opacity-0 group-hover:opacity-100 text-[12px]"
               onclick={() => deleteTask(task.id)}
               aria-label="Delete task"
             >
@@ -124,7 +124,7 @@
   <!-- Overflow -->
   {#if hasOverflow}
     <button
-      class="flex items-center gap-1.5 text-[11px] text-text-tertiary hover:text-text-secondary px-3"
+      class="flex items-center gap-1.5 text-[12px] text-text-secondary hover:text-text-secondary px-3"
       onclick={() => showOverflow = !showOverflow}
     >
       <ChevronDown size={12} class="transform {showOverflow ? 'rotate-180' : ''}" aria-hidden="true"
@@ -146,7 +146,7 @@
 
   <!-- WIP indicator -->
   {#if activeTasks.length > 0}
-    <p class="text-[10px] text-text-tertiary text-right">
+    <p class="text-[12px] text-text-secondary text-right">
       {Math.min(activeTasks.length, wipLimit)}/{wipLimit} active
     </p>
   {/if}