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/mcp/mcp_bridge.h

@@ -59,6 +59,7 @@ private:
     QJsonObject toolStatusSet(const QJsonObject& args);
     QJsonObject toolUiAction(const QJsonObject& args);
     QJsonObject toolTreeSearch(const QJsonObject& args);
+    QJsonObject toolNodeHistory(const QJsonObject& args);
 
     // Helpers
     QJsonObject makeTextResult(const QString& text, bool isError = false);