fix: DB completion path parsing, array-of-UDT resolution, blink source registration

- Fix path extraction pattern (missing closing quote, extra capture group)
- Add Array[..] of "UdtName" detection for nested member resolution
- Remove vim.schedule_wrap from DB member callback (causes blink.cmp timeout)
- Add built-in instruction parameter fallback (IEC_TIMER IN/PT/Q/ET)
- Ensure DB cache is populated on demand in completion source
- Make try_register() succeed without cmp.add_source_provider API
- docs: add blink.cmp source config steps to installation guide

lua/tia/blink_cmp_source.lua

@@ -239,10 +239,16 @@ function M:get_completions(context, callback)
     local db_parser = require("tia.db_parser")
     local db_name = active_portion:match('"([%w_]+)"')
     
+    -- Ensure cache is populated
+    if db_name and db_parser.get_cache_count() == 0 then
+      local ws = require("tia.workspace_types")
+      ws.scan_project_dbs(bufnr)
+    end
+    
     if db_name then
       local db = db_parser.get_db(db_name)
       if db then
-        local path = active_portion:match('"[^"]+%"%.([%w_.]*)')
+        local path = active_portion:match('"[^"]+"%.([%w_.]*)$')
         
         -- Resolve nested path through DB members
         local current_type = nil
@@ -269,15 +275,23 @@ function M:get_completions(context, callback)
             
             if found_member then
               resolved_path = part
+              local nested_type = nil
               if found_member.is_udt then
-                -- This member is a UDT type, continue resolving
+                nested_type = found_member.type
+              else
+                -- Check for array of UDT: Array[..] of "TypeName"
+                local array_udt = found_member.raw_type:match('Array%b[]%s*of%s*"([^"]+)"')
+                if array_udt then
+                  nested_type = array_udt
+                end
+              end
+              if nested_type then
                 local udt_parser = require("tia.udt_parser")
-                current_members = udt_parser.get_udt_members(found_member.type)
-                current_type = found_member.type
+                current_members = udt_parser.get_udt_members(nested_type)
+                current_type = nested_type
               else
                 -- This is a basic type, can't continue
                 if i < #path_parts then
-                  -- There are more parts but this isn't a UDT
                   found = false
                   break
                 end
@@ -319,14 +333,11 @@ function M:get_completions(context, callback)
               detail = m.raw_type,
             })
           end
-          local wrapped_callback = vim.schedule_wrap(function(response)
-            callback({
-              items = response.items,
-              is_incomplete_backward = false,
-              is_incomplete_forward = false,
-            })
-          end)
-          wrapped_callback({ items = items })
+          callback({
+            items = items,
+            is_incomplete_backward = false,
+            is_incomplete_forward = false,
+          })
           return
         end
       end
@@ -959,6 +970,28 @@ function M:get_completions(context, callback)
     end
 
     if not is_udt and not is_fb then
+      -- Check built-in instructions (IEC_TIMER, TON, etc.)
+      local builtin = require("tia.builtin_instructions")
+      local builtin_params = builtin.get_parameters(var_type)
+      if builtin_params then
+        local items = {}
+        for _, inp in ipairs(builtin_params.inputs or {}) do
+          table.insert(items, {
+            label = inp.name,
+            kind = vim.lsp.protocol.CompletionItemKind.Field,
+            detail = (inp.type or "ANY") .. " (Input)",
+          })
+        end
+        for _, out in ipairs(builtin_params.outputs or {}) do
+          table.insert(items, {
+            label = out.name,
+            kind = vim.lsp.protocol.CompletionItemKind.Field,
+            detail = (out.type or "ANY") .. " (Output)",
+          })
+        end
+        wrapped_callback({ items = items })
+        return
+      end
       wrapped_callback({ items = {} })
       return
     end