fix: improve code prompts to output only raw code

Add explicit instruction to all code generation prompts to return
only raw code without explanations, markdown, or code fences.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -1,3 +1,5 @@
+
+
+# Codetyper.nvim - AI coding partner files
+*.coder.*
 .coder/
-.*/.coder/.*
-**/*.coder.*