feat: add cron tool support and CLAUDE_CODE_DISABLE_CRON setting

Ticket 201

- Added format_tool_description entries for CronCreate, CronDelete,
  and CronList tools
- Added disable_cron field to ClaudeStartOptions and HikariConfig
- Pass CLAUDE_CODE_DISABLE_CRON=1 env var in both WSL and native
  spawn paths when disable_cron is enabled
- Added disable cron toggle to ConfigSidebar settings UI

src/lib/components/ConfigSidebar.svelte

@@ -58,6 +58,7 @@
     show_thinking_blocks: true,
     use_worktree: false,
     disable_1m_context: false,
+    disable_cron: false,
     max_output_tokens: null,
     trusted_workspaces: [],
     background_image_path: null,
@@ -549,6 +550,22 @@
         </p>
       </div>
 
+      <!-- Disable Cron Scheduling -->
+      <div class="mb-4">
+        <label class="flex items-center gap-3 cursor-pointer">
+          <input
+            type="checkbox"
+            bind:checked={config.disable_cron}
+            class="w-4 h-4 rounded border-[var(--border-color)] bg-[var(--bg-primary)] text-[var(--accent-primary)] focus:ring-[var(--accent-primary)]"
+          />
+          <span class="text-sm text-[var(--text-primary)]">Disable cron scheduling</span>
+        </label>
+        <p class="text-xs text-[var(--text-tertiary)] mt-1 ml-7">
+          Sets <code class="font-mono">CLAUDE_CODE_DISABLE_CRON=1</code> to prevent Claude from
+          scheduling recurring tasks
+        </p>
+      </div>
+
       <!-- Max Output Tokens -->
       <div class="mb-4">
         <label class="block text-sm text-[var(--text-primary)] mb-1" for="max-output-tokens">