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/editor.h

@@ -6,6 +6,7 @@
 #include <QPoint>
 #include <QHash>
 
+class QLineEdit;
 class QsciScintilla;
 class QsciLexerCPP;
 
@@ -154,6 +155,11 @@ private:
     const Provider* m_disasmRealProv = nullptr;   // real process provider — for reading code at arbitrary addresses
     const NodeTree* m_disasmTree = nullptr;
 
+    // ── Find bar ──
+    QLineEdit* m_findBar = nullptr;
+    void showFindBar();
+    void hideFindBar();
+
     // ── Reentrancy guards ──
     bool m_applyingDocument = false;
     bool m_clampingSelection = false;