feat: add builtin types/functions to diagnostics and completions

Files Modified/Created:
- src/builtin_instructions.lua - NEW: Contains all TIA Portal built-in types, FBs, and functions
- src/diagnostics.lua - Added missing data types + builtin instruction checking
- src/main.lua - Added completion support for built-in types/F Bs/functions
- src/plc_json.lua - Added .db file parsing + BOM handling fixes
- lua/scl/blink_cmp_source.lua - Extended completion with all built-in types/F Bs/functions
- src/node-types.json - Added node types for parser
- AGENTS.md - Updated documentation
Features Added:
1. Diagnostics - No more false "Unknown data type" warnings for:
   - All elementary types (USINT, SINT, UINT, UDINT, LINT, ULINT, TOD, DTL, etc.)
   - Timer/counter types (IEC_TON, TOF, TP, CTU, CTD, CTUD)
   - TIA Portal built-in FBs and functions
2. Auto-completion - Shows in VAR section after ::
   - 28 elementary data types
   - 23 built-in function blocks (TON, TOF, TP, CTU, CTD, CTUD, R_TRIG, F_TRIG, etc.)
   - 80+ built-in functions (ADD, SUB, MUL, DIV, SIN, COS, SQRT, etc.)

src/plc_json.lua

@@ -85,24 +85,33 @@ local function parse_scl_type_file(content)
   local current_type_name = nil
   local pending_type_name = nil
 
+  content = content:gsub("^([\239\187\191]+)", "")
+
   local lines = {}
   for line in content:gmatch("[^\n]+") do table.insert(lines, line) end
 
   for i, line in ipairs(lines) do
     local trimmed = line:gsub("^%s+", ""):gsub("%s+$", "")
 
-    if trimmed:match("^TYPE%s*:?%s*$") then
+    if trimmed:match("^TYPE%s") or trimmed:match('^TYPE"') or trimmed == "TYPE" then
       in_type = true
       in_struct = false
       current_type_name = nil
       pending_type_name = nil
+      local type_name = trimmed:match('TYPE%s+"([^"]+)"') or trimmed:match("^TYPE%s+(%w+)")
+      if type_name then
+        pending_type_name = type_name
+      end
+      in_struct = false
+      current_type_name = nil
+      pending_type_name = nil
     elseif trimmed:match("^END_TYPE") then
       in_type = false
       in_struct = false
       current_type_name = nil
       pending_type_name = nil
     elseif in_type then
-      if trimmed:match("^END_STRUCT") then
+      if trimmed:match("^END_STRUCT") or trimmed:match("^END_STRUCT;") then
         in_struct = false
         current_type_name = nil
         pending_type_name = nil
@@ -144,6 +153,48 @@ local function parse_scl_type_file(content)
   return types
 end
 
+local function parse_db_file(content)
+  local types = {}
+  local in_var = false
+  local current_type_name = nil
+
+  content = content:gsub("^([\239\187\191]+)", "")
+
+  local lines = {}
+  for line in content:gmatch("[^\n]+") do table.insert(lines, line) end
+
+  for i, line in ipairs(lines) do
+    local trimmed = line:gsub("^%s+", ""):gsub("%s+$", "")
+
+    if trimmed:match('^DATA_BLOCK%s+"([^"]+)"') then
+      current_type_name = trimmed:match('^DATA_BLOCK%s+"([^"]+)"')
+      types[current_type_name] = {
+        name = current_type_name,
+        kind = "struct",
+        fields = {},
+        source = "db_file",
+      }
+    elseif trimmed:match("^END_VAR") then
+      in_var = false
+    elseif trimmed:match("^VAR%s*$") or trimmed:match("^VAR ") then
+      in_var = true
+    elseif in_var and current_type_name and types[current_type_name] and trimmed ~= "" and not trimmed:match("^//") then
+      local field_name = line:match("^%s*(%w+)%s*:")
+      if field_name then
+        local field_type = line:match(":%s*([%w_]+)")
+        if field_type then
+          table.insert(types[current_type_name].fields, {
+            name = field_name,
+            type = field_type,
+          })
+        end
+      end
+    end
+  end
+
+  return types
+end
+
 function M.load_types_from_workspace(root_dir)
   local types = {}
 
@@ -213,6 +264,21 @@ function M.load_types_from_workspace(root_dir)
     end
   end
 
+  -- Also scan for .db files
+  local db_files = scan_files_recursive(root_dir, "*.db")
+  for _, filepath in ipairs(db_files) do
+    local content = run_command("cat " .. filepath:gsub(" ", "\\ "))
+    if content then
+      local db_types = parse_db_file(content)
+      for name, typ in pairs(db_types) do
+        typ.source = "db_file"
+        if not types[name] then
+          types[name] = typ
+        end
+      end
+    end
+  end
+
   return types
 end