feat(auth): add WebAuthn/Passkey support across all apps

Implements passwordless authentication via passkeys using @simplewebauthn:

Backend (mana-core-auth):
- New passkeys table in auth schema (credentialId, publicKey, counter, etc.)
- PasskeyService with registration/authentication flows and challenge storage
- 7 new API endpoints (register, authenticate, list, delete, rename)
- createSessionAndTokens helper for non-password auth flows
- Security event types for passkey operations

Client (shared-auth):
- signInWithPasskey() and registerPasskey() with dynamic @simplewebauthn/browser imports
- isPasskeyAvailable() browser capability check
- Passkey management methods (list, delete, rename)

UI (shared-auth-ui):
- Passkey button on LoginPage with key icon, shown when browser supports WebAuthn
- Divider between passkey and email/password form

App integration:
- All 19 web app auth stores have isPasskeyAvailable() and signInWithPasskey()
- All 19 web app login pages pass passkeyAvailable and onSignInWithPasskey props
- rpID=mana.how in production enables cross-app passkey usage (SSO-compatible)

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

packages/shared-auth/package.json

@@ -17,6 +17,7 @@
 	},
 	"dependencies": {
 		"@manacore/shared-types": "workspace:*",
+		"@simplewebauthn/browser": "^13.3.0",
 		"base64-js": "^1.5.1"
 	},
 	"devDependencies": {