Add user IdP linking and MFA setup modals

Implements endpoints and frontend modals for users to link/unlink external identity providers (IdPs) to their accounts, including backend logic for secure OAuth linking and session management. Adds ModalComponentMFASetup for multi-factor authentication setup, refactors modal input components for accessibility and consistency, and updates documentation and trademark policy. Adjusts scope constants and permissions for identity provider management.

TRADEMARK.md

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+# Endurain Trademark Policy
+
+_Last updated: 2025-10-17_
+
+"**Endurain**" (the **Word Mark**) is a claimed trademark of **João Vitória Silva** (the **Owner**).
+An application to register this word mark with the European Union Intellectual Property Office (EUIPO) is currently pending.  
+Until registration is granted, the mark should be referred to as **Endurain™**.
+
+The **Endurain logo** and related visual identity elements (the **Logos**) are original design works owned by João Vitória Silva and protected by copyright and design rights, but they are **not yet registered as separate trademarks**.
+
+This policy explains when and how you may use the Endurain name and Logos.  
+It exists alongside the software’s license (AGPLv3). **The AGPLv3 covers the code; this policy covers the branding.**
+
+## 1. Philosophy
+
+Endurain is open source and encourages self-hosting.  
+I want individuals, communities, and non-profits to freely use the **Endurain™** name and logo for non-commercial purposes.  
+At the same time, I reserve the right to control **commercial use** of the brand.
+
+## 2. Permitted Use Without Permission
+
+You **may** use the Endurain™ name and Logos in the following cases:
+
+- **Personal self-hosting** — running Endurain for yourself, friends, or family.  
+- **Community or club hosting** — for sports clubs, local groups, or other non-profit efforts.  
+- **Educational use** — teaching, research, or academic projects.  
+- **Open-source contributions** — forks, test deployments, and integrations, as long as they are not sold.  
+- **Nominative references** — talking about, writing about, or demonstrating Endurain truthfully.
+
+These uses may retain the name **Endurain™** and the official Logos.
+
+**Rules for non-commercial use:**
+- Do not imply that your use is officially sponsored or endorsed by the Endurain project.  
+- Do not alter the Logos except for reasonable resizing or adapting to backgrounds.  
+- Always comply with the AGPLv3 license for the code.  
+- Make it clear if your instance or fork is not the official Endurain service.
+
+## 3. Uses That Require Permission
+
+The following uses of the Endurain™ name or Logos require **prior written permission** from the Owner:
+
+- Offering **paid hosting**, **SaaS**, or commercial cloud services under the Endurain name.  
+- Selling products or services that prominently use the Endurain name or Logos.  
+- Using the Endurain name in a **company name, brand, or product line**.  
+- Marketing **commercial support, consulting, or training** under the Endurain name.  
+- Registering domains or social media handles that imply official status (e.g., `enduraincloud.com`, `@endurainapp`).  
+- Producing merchandise (shirts, stickers, etc.) with the Endurain name or Logos for sale.
+
+For permission requests, contact: [joao@endurain.com](mailto:joao@endurain.com).
+
+## 4. Forks and Distributions
+
+I welcome forks and distributions under the AGPLv3 license.  
+If your fork is **non-commercial**, you may keep the Endurain™ name and Logos, provided you:
+
+- Clearly state that it is **not the official Endurain project**.  
+- Identify it as “a fork of Endurain” or “based on Endurain.”  
+- Do not present yourself as an official maintainer or partner.
+
+If your fork is **commercial** (offering paid hosting, subscriptions, or products), you **must rename it** and **remove the Logos** unless you have written permission.
+
+## 5. Packages, Domains, and Namespaces
+
+- **Package registries** (npm, PyPI, Docker, etc.): Non-commercial packages may use “Endurain” in the name.  
+  Commercial or paid offerings may not without permission.  
+- **Domains and handles:** Avoid names that could be mistaken for the official project unless approved.
+
+## 6. Prohibited Uses
+
+The Endurain™ name and Logos may **never** be used:
+
+- In any misleading way that implies endorsement or partnership.  
+- In connection with illegal activities, malware, or harmful content.  
+- To promote or brand competing software as “Endurain” without permission.  
+- To sell any service or product under the Endurain name without authorization.
+
+## 7. License vs. Trademark
+
+The AGPLv3 license gives you broad rights to use, modify, and distribute the **code**, including commercially.  
+This trademark policy only limits how you use the **name and branding**.
+
+You are free to offer commercial services based on the Endurain code — but you must not market them **under the Endurain name or Logos** unless permitted.
+
+## 8. Attribution
+
+When referring to Endurain in permitted use, include the following notice:
+
+> "Endurain™ is a trademark of João Vitória Silva. Registration pending."
+
+## 9. Reporting Misuse
+
+If you believe the Endurain trademark or branding is being misused, please contact: [joao@endurain.com](mailto:joao@endurain.com).
+
+## 10. Changes
+
+This policy may be updated periodically. Any changes will be documented in this file.