feat: show AI progress and configure prompt directory

app/agentic.py

@@ -123,7 +123,9 @@ def load_prompt_templates(prompt_dir: Path) -> PromptTemplates:
             (prompt_dir / "USER.txt").read_text(encoding="utf-8")
         )
     except OSError as exc:
-        raise AgentError("Could not load prompts/MASTER.txt and prompts/USER.txt") from exc
+        raise AgentError(
+            f"Could not load {prompt_dir / 'MASTER.txt'} and {prompt_dir / 'USER.txt'}"
+        ) from exc
     if not master.strip() or not user.strip():
         raise AgentError("Prompt templates must not be empty")
     return PromptTemplates(master=master, user=user)