remove session_start startup notify

The "Pygienium loaded. Run /pygienium-help..." banner fired on every
session start. Drop it along with the PYGIENIUM_STARTUP_HINT constant
and the ExtensionContext/SessionStartEvent imports it alone consumed.

src/index.ts

@@ -26,9 +26,7 @@ import { homedir } from "node:os";
 import type {
 	ExtensionAPI,
 	ExtensionCommandContext,
-	ExtensionContext,
 	MessageRenderer,
-	SessionStartEvent,
 } from "@earendil-works/pi-coding-agent";
 import { Box, Text } from "@earendil-works/pi-tui";
 import "./checks/all.js";
@@ -40,10 +38,6 @@ import {
 } from "./phases.js";
 import type { AgentSessionEvent } from "@earendil-works/pi-coding-agent";
 
-/** Startup hint mirrored after piolium's convention. */
-export const PYGIENIUM_STARTUP_HINT =
-	"Pygienium loaded. Run /pygienium-help for available checks and flags.";
-
 /** Custom message type for the live tool-event stream (mirrors piolium-stream). */
 export const PYGIENIUM_STREAM = "pygienium-stream";
 
@@ -419,12 +413,4 @@ export default async function pygieniumExtension(
 			},
 		});
 	});
-
-	pi.on(
-		"session_start",
-		async (_event: SessionStartEvent, ctx: ExtensionContext) => {
-			if (!ctx.hasUI) return;
-			ctx.ui.notify(PYGIENIUM_STARTUP_HINT, "info");
-		},
-	);
 }