feat: value history timestamps, Ctrl+F search, base address fixes

- Add timestamps to ValueHistory ring buffer, expose via new MCP tool
  node.history, show relative time in popup ("26s ago", "2m ago")
- Add "Clear Value History" right-click menu for single and multi-select
- Add Ctrl+F find bar to RcxEditor with live search, Enter-to-next, wrap
- Fix Ctrl+F in workspace dock to auto-focus search field
- Add "Change to float" quick-convert for Hex32 right-click menu
- Sort workspace explorer by children count descending (most fields first)
- Fix provider->base() overwriting saved base address from .rcx files
- Add formula support to MCP change_base operation
- Re-evaluate baseAddressFormula on provider attach in selectSource()

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

src/workspace_model.h

@@ -46,10 +46,17 @@ inline void buildProjectExplorer(QStandardItemModel* model,
     auto nameOf = [](const Node* n) {
         return n->structTypeName.isEmpty() ? n->name : n->structTypeName;
     };
+    // Sort structs by children count descending (most fields first)
+    auto cmpChildren = [&](const Entry& a, const Entry& b) {
+        int ca = a.tree->childrenOf(a.node->id).size();
+        int cb = b.tree->childrenOf(b.node->id).size();
+        if (ca != cb) return ca > cb;
+        return nameOf(a.node).compare(nameOf(b.node), Qt::CaseInsensitive) < 0;
+    };
+    std::sort(types.begin(), types.end(), cmpChildren);
     auto cmpName = [&](const Entry& a, const Entry& b) {
         return nameOf(a.node).compare(nameOf(b.node), Qt::CaseInsensitive) < 0;
     };
-    std::sort(types.begin(), types.end(), cmpName);
     std::sort(enums.begin(), enums.end(), cmpName);
 
     // Helper: type display string for a member node