refactor(auth): centralize auth stores — 21 apps use createManaAuthStore factory

Created createManaAuthStore in @manacore/shared-auth-stores that replaces
~350 lines of duplicated auth.svelte.ts per app with a ~10 line factory call.

The factory handles: SSO, passkeys, 2FA, magic links, token management,
password reset, sign up/in/out — everything the old stores did.

Each app only provides devBackendPort and optional onAuthenticated callback.

Before: 21 apps × ~350 lines = 6,800 lines of duplicated auth code
After:  21 apps × ~10 lines  = 182 lines total (97% reduction)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-auth-stores/package.json

@@ -29,6 +29,7 @@
 		"typescript": "^5.0.0"
 	},
 	"dependencies": {
+		"@manacore/shared-auth": "workspace:*",
 		"@manacore/shared-types": "workspace:*"
 	}
 }