feat(jira): add editable jira_email field per user

Users can now set a separate Atlassian email for Jira authentication
in Settings → Profile → Jira Integration. Falls back to the Aegis
account email when not set, so existing setups are unaffected.

- Migration b043: adds jira_email column to users table
- User model/schema: expose jira_email read/write
- jira_service: _effective_jira_email() uses jira_email ?? email
- Frontend: replaces read-only email display with editable input

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

frontend/src/api/settings.ts

@@ -121,6 +121,8 @@ export interface UserPreferencesUpdate {
   notification_preferences?: Partial<NotificationPreferences>;
   jira_account_id?: string | null;
   jira_api_token?: string | null;
+  /** Atlassian email used for Jira auth. Overrides Aegis account email. Empty string clears it. */
+  jira_email?: string | null;
 }
 
 export interface UserMeOut {
@@ -134,6 +136,7 @@ export interface UserMeOut {
   last_login: string | null;
   notification_preferences: NotificationPreferences | null;
   jira_account_id: string | null;
+  jira_email: string | null;
   jira_token_set: boolean;
 }