Add account-settings OpenSpec change

Settings page at /settings with profile editing, passkey management
(list, add, delete), email change with verification, and account
deletion. Includes comprehensive E2E test plan using virtual WebAuthn.

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

openspec/changes/account-settings/proposal.md

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+## Why
+
+Users have no way to manage their account after registration. There's no
+settings page to edit their profile, manage passkeys, change email, or delete
+their account. Passkey count currently shows on the home page as a stopgap,
+but it belongs in a dedicated settings area.
+
+## What Changes
+
+- **Account settings page** (`/settings`): central place for account management
+- **Profile editing**: update display name and bio
+- **Email change**: update email with verification via magic link
+- **Passkey management**: view registered passkeys (device type, date added),
+  add new passkeys, delete existing ones
+- **Account deletion**: delete account and all associated data with confirmation
+- Move passkey status display from home page to settings
+
+## Capabilities
+
+### New Capabilities
+- `account-settings`: Settings page with profile, security, and account sections
+
+### Modified Capabilities
+- `journal-auth`: Passkey management moves from home page prompt to settings;
+  add passkey delete functionality
+
+## Impact
+
+- **Files**: New route `apps/journal/app/routes/settings.tsx`, API routes for
+  profile update, email change, passkey delete, account delete
+- **Database**: No schema changes — uses existing users and credentials tables
+- **Routes**: Must register new routes in `apps/journal/app/routes.ts`