feat(settings): add includeGitInstructions toggle

Adds an 'Include git instructions' toggle to the Agent Settings panel.
When disabled, sets CLAUDE_CODE_DISABLE_GIT_INSTRUCTIONS=1 on the Claude
process to remove built-in commit and PR workflow guidance from its
system prompt. Resolves #209.

src/lib/components/ConfigSidebar.svelte

@@ -59,6 +59,7 @@
     use_worktree: false,
     disable_1m_context: false,
     disable_cron: false,
+    include_git_instructions: true,
     max_output_tokens: null,
     trusted_workspaces: [],
     background_image_path: null,
@@ -566,6 +567,22 @@
         </p>
       </div>
 
+      <!-- Include Git Instructions -->
+      <div class="mb-4">
+        <label class="flex items-center gap-3 cursor-pointer">
+          <input
+            type="checkbox"
+            bind:checked={config.include_git_instructions}
+            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)]">Include git instructions</span>
+        </label>
+        <p class="text-xs text-[var(--text-tertiary)] mt-1 ml-7">
+          When disabled, sets <code class="font-mono">CLAUDE_CODE_DISABLE_GIT_INSTRUCTIONS=1</code> to
+          remove Claude's built-in commit and PR workflow guidance from its system prompt
+        </p>
+      </div>
+
       <!-- Max Output Tokens -->
       <div class="mb-4">
         <label class="block text-sm text-[var(--text-primary)] mb-1" for="max-output-tokens">