WebUI: resizable plots, digital/mixed modes, buffer fix, zoom brackets, updated docs

- Resizable plot grid: drag handles between plots adjust column/row fr sizes
- Plot configuration toolbar (click title): edit title, select Normal/Mixed/Digital mode
- Digital mode: logic-analyzer banded layout, signals quantized to hi/lo per band
- Mixed mode: banded layout where each signal is independently analog or digital
- Per-signal vscale toolbar embedded inline below plot header (badge click to open)
- Active signal highlighted in foreground with increased line width
- Signal offset markers draggable on Y axis; per-plot vscale state isolation
- Buffer sizing based on signal sampling rate (up to 60s @ configured rate)
- growBuffer: live buffer expansion without data loss on window/rate change
- Zoom bracket lines: nearest out-of-range points included for continuity
- Updated Docs/WebUI.md to reflect current uPlot-based implementation

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

Client/WebUI/static/index.html

@@ -188,6 +188,13 @@
           <label class="vstb-lbl">Pos</label>
           <input type="number" id="vscale-pos" class="ctx-num" step="0.1" value="0">
         </div>
+        <div id="vscale-type-row" style="display:none;align-items:center;gap:4px">
+          <label class="vstb-lbl">Type</label>
+          <div class="ctx-btns" id="vscale-type-btns">
+            <button class="ctx-btn active" data-type="analog">Analog</button>
+            <button class="ctx-btn" data-type="digital">Digital</button>
+          </div>
+        </div>
         <button id="btn-vscale-close" class="vstb-close" title="Close">✕</button>
       </div>
     </div>