Array element offset display, fold arrow UX, type picker popup, and provider cleanup

- Show relative hex offset on array element separators ([N] +0x...)
- Dim fold arrows and add hover highlight for better visibility
- Extend fold/chevron click areas for easier interaction
- Add type picker popup for array element type and pointer target editing
- Remove process_provider.h in favor of plugin-based provider system
- Expand compose/format to handle struct-of-array type names and widths

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

src/providers/provider.h

@@ -40,7 +40,7 @@ public:
 
     // Resolve an absolute address to a symbol name.
     // Returns empty string if no symbol is known.
-    // ProcessProvider: "ntdll.dll+0x1A30"
+    // Example: "ntdll.dll+0x1A30"
     // BufferProvider: "" (no symbols in flat files)
     virtual QString getSymbol(uint64_t addr) const {
         Q_UNUSED(addr);