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>

backend/app/models/user.py

@@ -31,3 +31,4 @@ class User(Base):
     notification_preferences = Column(JSONB, nullable=True, server_default='{"email_on_test_validated": true, "email_on_campaign_completed": true, "email_on_new_mitre_techniques": false, "in_app_all": true}')
     jira_account_id = Column(String(100), nullable=True)
     jira_api_token = Column(String(500), nullable=True)   # personal Atlassian token
+    jira_email = Column(String(255), nullable=True)        # Atlassian email (overrides account email)