refactor(login): organize login routes and components by forge

[afonsojramos]

Summary

The PAT login route comingled GitHub and Gitea logic through isGitea conditionals. Now that forge adapters exist, this organizes the login components and routes the same way: forge-specific knowledge lives in forge-specific modules, and shared code stays free of forge branching.

• Extract the shared PAT form shell into components/login/LoginWithPersonalAccessTokenForm, which owns form state, validation, and submission. Forge-specific copy is supplied via props, and the GitHub-only recommended-scopes hint renders through a children slot, so the shared form contains zero forge conditionals.
• Add forge-specific login route components organized like utils/forges/<forge>/:
  • routes/github/LoginWithPersonalAccessToken and routes/gitea/LoginWithPersonalAccessToken supply their own copy to the shared form.
  • routes/github/LoginWithDeviceFlow and routes/github/LoginWithOAuthApp move under routes/github/ since GitHub is the only forge with those capability bundles; they no longer read the forge from router state.
• Register forge-specific paths: /login/github/device-flow, /login/github/personal-access-token, /login/github/oauth-app, /login/gitea/personal-access-token.
• LoginMethodDescriptor gains a required authMethod and drops the router state field (LoginRouteState is deleted). With routes being forge-specific, no forge needs to travel through navigation state anymore; re-auth still passes the account.
• Accounts is now fully adapter-driven: the "Add new account" menu renders from listAdapters() × loginMethods (existing testids preserved), and re-authentication resolves its destination via the account's adapter descriptor instead of a hardcoded switch. An unmatched auth method now logs an error instead of silently doing nothing.

Adding a new forge (e.g. Bitbucket) no longer touches any shared login component: register the adapter, add its route components, and the login screen, add-account menu, and re-auth flow pick it up.

User-visible changes

• Add-account menu labels are now consistently Login with <forge> (<method>), so the GitHub PAT and OAuth App entries read "Login with GitHub (Personal Access Token)" and "Login with GitHub (OAuth App)". Reproducing the old inconsistent labels would have required reintroducing a forge conditional.
• The Gitea menu entry now shows the key icon from its login-method descriptor (matching the login screen) instead of the server icon.

Testing

• PAT route tests split per forge with new Gitea coverage (token format validation, token settings URL, login payload including forge: 'gitea').
• New re-authentication tests covering all auth methods across both forges, previously untested.
• Add-account menu tests now also lock the menu labels.
• Full suite: 145 files / 1082 tests passing, lint, format, and typecheck clean.

Closes #2866

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
97.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud