Animation None option, FPS min 1, serial COM lifecycle fixes

- Replace animation Enable checkbox with None option in effect selector;
  show effect description tooltip; disable speed slider when None selected
- Allow target FPS range 1-90 (was 10-90) across UI and backend validation
- Scope serial COM connections to target lifetime (no idle caching);
  use temporary connections for power-off/test mode
- Fix serial black frame on stop: flush after write, delay after task
  cancel to prevent race with in-flight thread pool write

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/templates/modals/stream.html

@@ -41,9 +41,9 @@
                             <label for="stream-target-fps" data-i18n="streams.target_fps">Target FPS:</label>
                             <button type="button" class="hint-toggle" onclick="toggleHint(this)" title="?">?</button>
                         </div>
-                        <small class="input-hint" style="display:none" data-i18n="streams.target_fps.hint">Target frames per second for capture (10-90)</small>
+                        <small class="input-hint" style="display:none" data-i18n="streams.target_fps.hint">Target frames per second for capture (1-90)</small>
                         <div class="slider-row">
-                            <input type="range" id="stream-target-fps" min="10" max="90" value="30" oninput="document.getElementById('stream-target-fps-value').textContent = this.value">
+                            <input type="range" id="stream-target-fps" min="1" max="90" value="30" oninput="document.getElementById('stream-target-fps-value').textContent = this.value">
                             <span id="stream-target-fps-value" class="slider-value">30</span>
                         </div>
                     </div>