Fix GitHub Enterprise host identity loss across PR/work-item paths

- Thread `host` through mobile PR RPC params, IPC work-item lookups, and
  RPC schemas so GHES identity survives the renderer/mobile/main boundary
  instead of silently falling back to a same-named github.com repo.
- Qualify `--repo`/`-R` args for github.com too (not just GHES), since
  gh resolves bare shorthand against a process-level GH_HOST that can
  redirect pinned github.com commands.
- Cache `getOriginGitHubApiRepository` to avoid a per-call uncached
  `git remote get-url` round trip on connection-backed repos.
- Add a local-fork fallback in `getWorkItemDetails` so PRs living on a
  base repo (not visible via the origin slug) still resolve via cwd.
- Centralize the github.com-vs-GHES host predicate in
  `isDefaultGitHubHost` so cache keys, quota scoping, and identity
  checks can't drift out of sync.

src/main/github/client-pr-local-runtime.test.ts

@@ -122,6 +122,14 @@ import {
   updatePRTitle
 } from './client'
 
+import { _resetOriginGitHubApiRepositoryCache } from './github-api-repository'
+
+// The origin-repository cache is module-level state; reset it so slugs
+// resolved by one test cannot leak into the next.
+beforeEach(() => {
+  _resetOriginGitHubApiRepositoryCache()
+})
+
 describe('GitHub PR local runtime routing', () => {
   beforeEach(() => {
     execFileAsyncMock.mockReset()