feat: update max_output_tokens upper bound and helper text for 128k (#231)

Adds max="128000" to the config input and updates the placeholder and
helper text to reflect the new per-model limits from CLI v2.1.77.

src/lib/components/ConfigSidebar.svelte

@@ -610,13 +610,15 @@
           id="max-output-tokens"
           type="number"
           min="1"
-          placeholder="Default (32000)"
+          max="128000"
+          placeholder="Default (model-dependent)"
           bind:value={config.max_output_tokens}
           class="w-full px-3 py-2 text-sm bg-[var(--bg-primary)] border border-[var(--border-color)] rounded text-[var(--text-primary)] placeholder-[var(--text-tertiary)] focus:outline-none focus:border-[var(--accent-primary)]"
         />
         <p class="text-xs text-[var(--text-tertiary)] mt-1">
-          Sets <code class="font-mono">CLAUDE_CODE_MAX_OUTPUT_TOKENS</code> — increase if responses are
-          being cut off mid-reply
+          Sets <code class="font-mono">CLAUDE_CODE_MAX_OUTPUT_TOKENS</code>. Maximum: 128k tokens
+          for Opus 4.6 and Sonnet 4.6 (64k default for Opus 4.6, 32k for other models). Increase if
+          responses are being cut off.
         </p>
       </div>