agent: embed reasoning and memory skills into system prompt at render time

Read ollie/sk/reasoning.md and ollie/sk/memory.md from the 9P mount
and append them to the rendered system prompt. Removes dependency on
the model following a startup instruction.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/agent/core.go

@@ -46,6 +46,19 @@ func systemPrompt(cwd string) string {
 		"IsGitRepo": "unknown",
 		"SessionID": os.Getenv("OLLIE_SESSION_ID"),
 	})
+
+	mount := os.Getenv("OLLIE_9MOUNT")
+	if mount == "" {
+		home, _ := os.UserHomeDir()
+		mount = home + "/mnt/ollie"
+	}
+	for _, skill := range []string{"reasoning", "memory"} {
+		data, err := os.ReadFile(mount + "/sk/" + skill + ".md")
+		if err == nil {
+			fmt.Fprintf(&buf, "\n\n---\n\n%s", data)
+		}
+	}
+
 	return buf.String()
 }