single source of truth for pi config via ~/.pi/agent

auth.json stores api keys, models.json stores local providers directly.
no more copies, sync layers, or per-user config generation.
docker containers mount pi config read-only.

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

src/servers/data-path.ts

@@ -1,10 +1,11 @@
 import { join, resolve } from 'node:path';
+import { homedir } from 'node:os';
 
 export const DATA_PATH = process.env.DATA_PATH ?? join(process.cwd(), 'data');
 
 export const SERVER_CONFIG_DIR = join(DATA_PATH, 'server-settings');
 
-export const PI_CONFIG_DIR = join(DATA_PATH, 'pi-config');
+export const PI_CONFIG_DIR = join(homedir(), '.pi', 'agent');
 
 export const SEED_PATH = resolve(import.meta.dir, '../../seed');