GPT-5.6 Luna vs GPT-5.6 Sol for vibe coding

- Add explicit labels for bill and percentage controls to improve accessibility.
- Validate bill input and constrain it to nonnegative currency values.
- Replace fragile implicit element globals with explicit DOM lookups and `textContent`.

```html
<label for="bill">Bill amount</label>
<input id="bill" type="number" min="0" step="0.01" required>
<label for="pct">Tip percentage</label>
<select id="pct">
  <option>10</option>
  <option>15</option>
  <option>20</option>
</select>
<button onclick="calc()">Go</button>
<p id="out"></p>
<script>
funct…

- Add accessible labels for bill amount and tip percentage.
- Reject empty, non-finite, or negative bill amounts with a clear message.
- Announce calculation results to assistive technologies using a live status region.

```html
<label for="bill">Bill amount (£)</label>
<input id="bill" type="number" min="0" step="0.01">

<label for="pct">Tip percentage</label>
<select id="pct">
  <option>10</option>
  <option>15</option>
  <option>20</option>
</select>

<button onclick="calc()">Go</button>
<p id="out" role="status" aria-live="polite"></p>

<sc…