docs: encourage adding comments; fix nested IF/ELSIF indentation

- Update AGENTS.md to encourage comments instead of forbidding them
- Add docstrings to all public functions in src/ modules
- Add module headers and function comments to lua/scl/ modules
- Fix formatter to properly indent multi-line IF/ELSIF conditions
- Fix FB call detection to not match IF statements with parentheses

lua/scl/db_parser.lua

@@ -3,10 +3,30 @@
 
 local M = {}
 
+-- Cache for parsed DBs: { [db_name] = db_definition }
 local db_cache = {}
 
+-- Inline DB definitions (from comments): { [db_name] = db_definition }
 local inline_dbs = {}
 
+-- DB Definition structure:
+-- {
+--   name = "DBName",
+--   title = "Data Block Title",
+--   version = "0.1",
+--   comment = "User comment",
+--   members = {
+--     {
+--       name = "memberName",
+--       type = "Bool" or '"OtherUdt"',
+--       attributes = "{ S7_SetPoint := 'True' }",
+--       comment = "Member comment",
+--       is_udt = false -- true if type is a quoted UDT reference
+--     }
+--   }
+-- }
+
+-- Register an inline DB definition (from comments or other sources)
 function M.register_inline_db(db)
   if db and db.name then
     inline_dbs[db.name] = db