Inline edit UX improvements: selection clamping, auto-select, validation fixes

- Constrain selection/cursor to edit span boundaries during inline edit
- Auto-select entire text when entering edit mode (Name, Value, Type)
- Double-click during edit selects entire editable text
- Fix vector component validation (subLine >= 0 for x component)
- Accept EU decimal separator (comma) for float parsing
- Darker selection highlight (35,35,35) vs hover (43,43,43)
- Remove blue text indicator, use hidden style
- Fix validation error message display

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/editor.h

@@ -116,6 +116,7 @@ private:
     void applyHoverHighlight();
     void validateEditLive();
     void setEditComment(const QString& comment);
+    void clampEditSelection();
 
     // ── Refactored helpers ──
     struct HitInfo { int line = -1; int col = -1; uint64_t nodeId = 0; bool inFoldCol = false; };