Add user profile editing page

[sergeychernyshev]

This PR adds a comprehensive user profile editing and management experience, with a fully decentralized and provider-partitioned identity management system, and refactored internal communication using RPC.

Key changes:

• Created public/users/profile.html for editing user name and managing credentials.
• RPC Refactoring: Refactored all Durable Objects (UserDO, AccountDO, SystemDO, CredentialDO) to use direct RPC method calls instead of fetch(). This improves performance and developer experience for internal system communication.
• Provider-Partitioned Credentials: Refactored CredentialDO to be identified solely by provider (e.g., one DO for "google", one for "twitch"). Each instance stores all credentials for that provider, enabling efficient global lookups.
• Decentralized Identity Mapping: Each UserDO now maintains its own list of linked credentials, removing centralized mappings from SystemDO.
• Refined Data Handling: User avatars and primary profile details are now only fetched and stored during initial account creation, ensuring a stable user identity when linking multiple OAuth providers.
• Account Linking: Users can link multiple OAuth identities to a single account, with full management (listing/removal) on the profile page.
• Added a safeguard to prevent users from deleting their last remaining login method.
• Made the user's name in the power-strip component a link to the profile page.
• Implemented instant UI refresh of the power-strip after profile updates.
• Added comprehensive integration tests for the finalized decentralized RPC-based architecture.
• Documentation: Updated architecture documentation and Mermaid diagrams to reflect the provider-partitioned model.

Closes #61

✨ Assisted by AI: Gemini

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Status	Name	Latest Commit	Updated (UTC)
❌ Deployment failed View logs	startup-api	14d63ac	Feb 17 2026, 02:21 AM