feat(auth)!: require an explicit callback path

[humandebri]

Purpose

• let native clients choose one shared HTTPS authentication callback path

Changes

• require callbackPath when constructing the Internet Identity authenticator
• use the configured path for authorization URLs, callback matching, and response validation
• reject invalid and obsolete callback paths in regression tests

Verification

• swift test
• xcodebuild -scheme ICNativeClient -destination "generic/platform=iOS Simulator" build

Impact

• breaking API change; callers must pass callbackPath

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.