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/multiline_params.lua

@@ -1,5 +1,11 @@
+-- Multiline parameter filling for SCL function block calls
+-- Automatically expands FB calls to multi-line format with all parameters
+
 local M = {}
 
+--- Get interface for built-in FB types (TON, TOF, etc.)
+--- @param var_type string The FB type name
+--- @return table|nil Interface with inputs, outputs, inouts
 local function get_builtin_interface(var_type)
   local builtin = require("scl.builtin_instructions")
   local clean_type = var_type:gsub('"', ''):gsub("#", ""):upper()
@@ -14,6 +20,9 @@ local function get_builtin_interface(var_type)
   return nil
 end
 
+--- Get interface for custom FB types from workspace
+--- @param var_type string The FB type name
+--- @return table|nil Interface with inputs, outputs, inouts
 local function get_fb_interface(var_type)
   local fb_parser = require("scl.fb_parser")
   local clean_type = var_type:gsub('"', '')
@@ -26,6 +35,9 @@ local function get_fb_interface(var_type)
   return fb_parser.get_fb_interface(clean_type)
 end
 
+--- Check if a type is a known FB type
+--- @param var_type string The type name to check
+--- @return boolean True if type is an FB
 local function is_fb_type(var_type)
   local fb_parser = require("scl.fb_parser")
   local clean_type = var_type:gsub('"', '')
@@ -38,6 +50,9 @@ local function is_fb_type(var_type)
   return fb_parser.is_fb_type(clean_type)
 end
 
+--- Get list of known local variable names
+--- @param bufnr number Buffer number
+--- @return table Set of variable names
 local function get_known_variables(bufnr)
   local scl_vars = require("scl.variables")
   local variables = scl_vars.extract_variables(bufnr)
@@ -48,11 +63,17 @@ local function get_known_variables(bufnr)
   return known
 end
 
+--- Get the type of a variable by name
+--- @param var_name string Variable name
+--- @param bufnr number Buffer number
+--- @return string|nil Variable type, or nil if not found
 local function get_variable_type(var_name, bufnr)
   local scl_vars = require("scl.variables")
   return scl_vars.get_variable_type(var_name, bufnr)
 end
 
+--- Fill multiline parameters for FB call at cursor
+--- Expands single-line call to multi-line with all parameters
 function M.fill_multiline_params()
   local bufnr = vim.api.nvim_get_current_buf()
   local cursor = vim.api.nvim_win_get_cursor(0)
@@ -169,6 +190,11 @@ function M.fill_multiline_params()
   vim.api.nvim_win_set_cursor(0, { new_cursor_row, new_cursor_col })
 end
 
+--- Check if cursor is inside an FB call parameter list
+--- @param bufnr number Buffer number
+--- @param cursor_row number Current row (1-based)
+--- @param cursor_col number Current column (1-based)
+--- @return boolean True if inside FB call params
 local function is_inside_fb_call(bufnr, cursor_row, cursor_col)
   local function get_line_text(rownum)
     return vim.api.nvim_buf_get_lines(bufnr, rownum - 1, rownum, false)[1] or ""
@@ -214,6 +240,9 @@ local function is_inside_fb_call(bufnr, cursor_row, cursor_col)
   return false
 end
 
+--- Jump to next parameter in FB call
+--- Used for Tab navigation within parameter lists
+--- @return boolean True if jumped to next param, false otherwise
 function M.jump_to_next_param()
   local cursor = vim.api.nvim_win_get_cursor(0)
   local row = cursor[1]