fix: migrate default NGA backend

[BugenZhao]

What changed

• Change the default NGA backend from nga.178.com to bbs.nga.cn in Rust logic and Swift URL defaults.
• Migrate persisted empty or legacy https://nga.178.com backend settings to the new default.
• Update backend picker options to prefer currently working NGA hosts.

Why

nga.178.com now redirects API traffic to bbs.nga.cn. MNGA sends auth through POST form fields, and the redirect path can lose those fields before the request reaches the final host, causing NGA to report 未登录 or request errors.

Validation

• cargo fmt
• cargo test -p service request::test::test_normalize_base_url -- --exact
• cargo test -p service test_topic_list -- --ignored --nocapture
• cargo clippy

[Copilot]

Pull request overview

Updates MNGA’s default NGA backend to avoid redirect-related auth loss by switching the default host from nga.178.com to bbs.nga.cn, and migrates stored legacy/empty backend settings to the new default across both the Rust logic module and the Swift app.

Changes:

• Change Rust logic default DEFAULT_BASE_URL to https://bbs.nga.cn and migrate legacy/empty persisted base URLs during set_request_option.
• Update Swift URL defaults and backend picker host list, plus migrate persisted legacy/empty backend settings on app startup.
• Simplify CI tool installation by using jdx/mise-action to provision tuist instead of Homebrew formula installation.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
logic/service/src/request.rs	Adds legacy/empty base URL normalization and a focused unit test.
logic/service/src/constants.rs	Switches Rust logic default backend host to bbs.nga.cn.
app/Shared/Utilities/WhatsNew.swift	Bumps “What’s New” entry version to 2.3.1.
app/Shared/Utilities/URLs.swift	Updates Swift default backend host and curated host options list.
app/Shared/Storage/PreferencesStorage.swift	Migrates stored backend setting when empty or pointing at the legacy host.
app/Project.swift	Bumps MARKETING_VERSION to 2.3.1.
.github/workflows/release.yaml	Uses mise-action to install tuist instead of Homebrew.
.github/workflows/ios_debug.yaml	Uses mise-action to install tuist instead of Homebrew.

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