fix: find with plain=true makes ^ literal, breaking all prefix matching

Nine sites used name:upper():find('^' .. prefix:upper(), 1, true).
With plain=true, '^' is treated as a literal character, so the prefix
was never found and no variables/params ever matched the typed text.

Replaced all with substring comparison:
  name:upper():sub(1, #prefix) == prefix:upper()

This fixes:
- Variable completion without # prefix (instTestTimer never matched)
- Function parameter filtering by typed prefix (IN never matched IN)
- # trigger variable filtering

src/main.lua

@@ -759,7 +759,7 @@ end
 local function add_param_items(items, params, prefix_filter)
 	for _, inp in ipairs(params.inputs or {}) do
 		local label = inp.name .. " := "
-		if prefix_filter == "" or inp.name:upper():find("^" .. prefix_filter:upper(), 1, true) then
+		if prefix_filter == "" or inp.name:upper():sub(1, #prefix_filter) == prefix_filter:upper() then
 			table.insert(items, {
 				label = label,
 				kind = 13,
@@ -771,7 +771,7 @@ local function add_param_items(items, params, prefix_filter)
 	end
 	for _, out in ipairs(params.outputs or {}) do
 		local label = out.name .. " => "
-		if prefix_filter == "" or out.name:upper():find("^" .. prefix_filter:upper(), 1, true) then
+		if prefix_filter == "" or out.name:upper():sub(1, #prefix_filter) == prefix_filter:upper() then
 			table.insert(items, {
 				label = label,
 				kind = 13,
@@ -835,7 +835,7 @@ function handlers.textDocument_completion(params)
 			if doc.variables then
 				local prefix = has_hash_prefix and line_before:match("#([%w_]*)$") or word_prefix
 				for name, info in pairs(doc.variables) do
-					if prefix == "" or name:upper():find("^" .. prefix:upper(), 1, true) then
+					if prefix == "" or name:upper():sub(1, #prefix) == prefix:upper() then
 						table.insert(items, {
 							label = "#" .. name,
 							filterText = "#" .. name,
@@ -972,7 +972,7 @@ function handlers.textDocument_completion(params)
 				-- Add declared variables (label without # so client-side matching works)
 				if doc.variables then
 					for name, info in pairs(doc.variables) do
-						if word_prefix == "" or name:upper():find("^" .. word_prefix:upper(), 1, true) then
+						if word_prefix == "" or name:upper():sub(1, #word_prefix) == word_prefix:upper() then
 							table.insert(items, {
 								label = name,
 								filterText = name,
@@ -1006,7 +1006,7 @@ function handlers.textDocument_completion(params)
 				-- Add declared variables in general context too
 				if doc.variables then
 					for name, info in pairs(doc.variables) do
-						if word_prefix == "" or name:upper():find("^" .. word_prefix:upper(), 1, true) then
+						if word_prefix == "" or name:upper():sub(1, #word_prefix) == word_prefix:upper() then
 							table.insert(items, {
 								label = name,
 								filterText = name,