[SETTINGS-01] Complete company, integration and AI settings

[Krisor1986]

Goal

Complete all settings sections shown in the approved views.

Tasks

• Company profile and dynamic company name
• Appearance, theme and interface density
• Language settings
• Users and permissions
• Integrations
• AI agents and knowledge configuration
• Security settings
• Visible save success and error feedback

Acceptance criteria

• Every settings tab displays relevant content
• Saved changes persist after refresh
• Buttons always show a success or error reaction

Dependencies

• [APP-SHELL-01]
• [I18N-01]