feat: include is_new_user in frontend callback URL

[think-in-universe]

Include is_new_user into frontend callback URL of OAuth login, which is required by PostHog integration

• https://{frontend_base_url}/auth/callback?token={}&expires_at={}&is_new_user=true

[Copilot]

Pull Request Overview

This PR modernizes the Rust codebase by updating string formatting to use inline format syntax, adds an is_new_user flag to OAuth callbacks, and introduces a Rust toolchain configuration file.

Key Changes:

• Added rust-toolchain.toml to specify Rust version 1.88.0 and required components
• Enhanced OAuth callback flow to track and return whether a user is new or existing
• Replaced legacy format!("{}", var) syntax with modern inline format syntax format!("{var}")

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rust-toolchain.toml	Specifies Rust toolchain version and components
crates/services/src/types.rs	Updated test to use inline format syntax
crates/services/src/auth/service.rs	Added is_new_user tracking in OAuth flow and updated formatting
crates/services/src/auth/ports.rs	Updated OAuthService trait signature to include is_new_user
crates/api/tests/e2e_api_tests.rs	Modernized format strings and println statements
crates/api/src/routes/oauth.rs	Added is_new_user to callback URL query parameters
crates/api/src/routes/api.rs	Updated format strings and improved range check idiom
crates/api/src/middleware/auth.rs	Modernized format strings in logging statements
crates/api/src/main.rs	Updated error message format string
crates/api/src/error.rs	Simplified OAuth provider error message formatting

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[Copilot]

Pull Request Overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated no new comments.

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