feat: add interactive attribute block toggle with keybindings and commands

Add ability to expand/collapse SCL variable attribute blocks like {EXTERNALACCESSIBLE := 'false'} to {...}

Features:
- Per-variable collapse rules via collapseVariableRules option
- Interactive toggle with <Leader>xa keybinding
- Commands: SCLToggleAttrBlock, SCLExpandAllAttrBlocks, SCLCollapseAllAttrBlocks
- Keybindings: <Leader>xa (toggle), <Leader>xae (expand all), <Leader>xac (collapse all)
- Supports both formatter-collapsed and manually collapsed blocks

Also update AGENTS.md with new documentation and troubleshooting guide

src/parser.lua

@@ -78,15 +78,26 @@ function M.extract_variables(content)
       return
     end
 
-    local var_name = trimmed:match("^([%w_]+)%s*:")
+    local var_name = trimmed:match("^([%w_]+)%s*%b{}%s*:") or trimmed:match("^([%w_]+)%s*:")
     if not var_name then
-      var_name = trimmed:match("^([%w_]+)%s*,")
+      var_name = trimmed:match("^([%w_]+)%s*%b{}%s*,") or trimmed:match("^([%w_]+)%s*,")
     end
 
     if var_name and not variables[var_name] then
       local col = line:find(var_name, 1, true)
       if col then
-        local type_start = line:find(":", 1, true)
+        local type_start = nil
+        local brace_depth = 0
+        for i = 1, #line do
+          local c = line:sub(i, i)
+          if c == "{" then
+            brace_depth = brace_depth + 1
+          elseif c == "}" then
+            brace_depth = brace_depth - 1
+          elseif c == ":" and brace_depth == 0 then
+            type_start = i
+          end
+        end
         local var_data_type = "unknown"
         if type_start then
           local type_part = line:sub(type_start + 1)