feat(phase9): relocate sparkline toggle from Rituals to Tasks section

Phase 8 carryover backlog: the showMomentumSparkline toggle was
sitting under Rituals and visually claimed by the Launch-at-login
border-t subgroup. New top-level Tasks section hosts it, ready to
absorb future task-page settings (energy default, WIP limit, etc.).

The deeper Phase 9 SettingsPage restructure (search box + 7-group
progressive disclosure via the new SettingsGroup component) is
deferred to a follow-up polish session: the existing 2309-line file
uses a hand-rolled accordion that needs careful unwinding, and is
not in this session's scope. SettingsGroup component remains
available for that future pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/pages/SettingsPage.svelte

@@ -1530,6 +1530,27 @@
               </div>
             </div>
 
+          </div>
+        {/if}
+      </div>
+
+      <!-- Tasks (Phase 9 — relocated from Rituals to its own section).
+           Houses the gamification sparkline toggle and any future
+           task-page-specific settings. -->
+      <div class="border-b border-border-subtle">
+        <button
+          class="flex items-center justify-between w-full py-4 px-5 text-left"
+          onclick={() => openSection = openSection === 'tasks' ? null : 'tasks'}
+        >
+          <h3 class="font-display text-[18px] italic text-text">Tasks</h3>
+          <span class="text-text-tertiary text-[16px] leading-none">{openSection === 'tasks' ? '−' : '+'}</span>
+        </button>
+        {#if openSection === 'tasks'}
+          <div class="px-5 pb-5 animate-fade-in">
+            <p class="text-[11px] text-text-tertiary mb-4">
+              How the Tasks page surfaces progress. Always additive.
+            </p>
+
             <!-- Phase 8: forgiving gamification. Toggle controls the sparkline only.
                  The "N today" badge on the Tasks header is always on. -->
             <Toggle