M6: Discussions & Projects (GraphQL) + Auto-merge

[michaeljolley]

Part of the RayCast parity roadmap. Stacked on top of #292 (M5).

What this adds

Introduces a minimal GraphQL client alongside the Octokit REST client to reach capabilities REST does not expose.

• GraphQL foundation: GitHubGraphQLClient / IGitHubGraphQLClient POST queries + mutations using the signed-in developer's OAuth token. The GraphQL endpoint is derived from the REST base address, so github.com works today and GHES (M8) will work once the host is configurable.
• Discussions (My + Search): \DiscussionsPage\ is a \DynamicListPage; the user types a search query and results come from GraphQL \search(type: DISCUSSION). Top-level My Discussions (\�uthor:@me) and Search Discussions commands.
• Projects (My): \ProjectsPage\ lists the signed-in user's Projects v2 via \�iewer.projectsV2. Top-level My Projects command.
• Enable/Disable Auto-merge (deferred from M3): GraphQL-only mutation. \GitHubAutoMergeManager\ resolves the PR node id then calls \�nablePullRequestAutoMerge\ / \disablePullRequestAutoMerge. Wired into \MutationCommandsFactory\ so open PRs now offer Enable and Disable auto-merge.
• Discussions/Projects icons, ResW strings, composition-root wiring.

Tests

• Endpoint resolution (github.com + GHES), discussion/project mapping, auto-merge resolve-then-mutate, page rendering.
• 201/201 tests pass.

Notes

• Discussions/Projects are live-fetch (like Notifications/Workflow Runs), kept out of the search-keyed SQLite cache.
• Both Enable and Disable auto-merge are offered since current auto-merge state is not queried up front.