Feat: Add runtime PAT entry with user avatar. [draft B]

[matejvasek]

In this attempt I removed:

"SourceControlService interface extended with init(pat: string) and isInitialized(): boolean methods; GithubService implementation updated accordingly",

to give Claude more freedom

Changes

• Replace compile-time GitHub PAT injection (webpack DefinePlugin) with runtime entry via a modal that validates the PAT against the GitHub API and stores it in sessionStorage
• Add UserAvatar component to every page header showing the authenticated GitHub user (clickable on list page, display-only on create/edit)
• Disable Create button until a PAT is provided, with tooltip and hint alert when the modal is dismissed without one
• Add PatContext (React Context) for cross-cutting PAT state, rewrite useSourceControlService to read PAT from context instead of a baked-in global
• Remove GITHUB_PAT from webpack DefinePlugin and globals.d.ts

The PAT was previously required at build time and baked into the bundle. Now users enter it at runtime on first visit. sessionStorage keeps it for the browser session. Each view wraps itself with a PatProvider since OCP dynamic plugins render routes independently.

New files: PatContext, useUserAvatar, PatModal, UserAvatar, PageWrapper. 12 test suites, 65 tests passing.