fix(worktree): run the create-base warm-up on the routed git host (#17794)

The speculative warm-up that runs while the create composer is open resolved
refs and fetched with host Git even when the project's runtime is a WSL distro,
while both the checkout preparation it feeds (`prepareWorktreeCreateForRepo`,
which already resolves `{ wslDistro }` itself) and the real create path run
inside the distro.

The concrete cost was a discarded fetch: `getCanonicalFetchKey` namespaces the
runtime's remote-fetch cache `wsl:<distro>` vs `local`, so the warm-up's fetch
landed in a namespace create never looks at, and create fetched again. On a
Windows host with no usable host-side Git the probes also failed outright, so
that cohort got no warm-up at all.

Thread the project's worktree Git options through the prefetch (resolved by a
non-throwing helper, because an optimistic warm-up must not surface a
repair-required runtime as a failure) so every probe and fetch runs where create
runs. `gitOptions` is a required argument, so a caller cannot drop the routing
silently. Host-routed calls keep their original arity, so macOS, Linux,
native-Windows-host projects, SSH repos and folder workspaces are unchanged.

Narrower than it looks: for a repo under \\wsl.localhost\<distro>\... the probes
were already routed by cwd, and for a repo on a Windows drive letter host Git
and WSL Git read the same on-disk repository, so the answers were already
correct there. What those cohorts gain is a fetch create can reuse; what they
pay is that the probes now run inside the distro (over /mnt/c for drive-letter
repos, which also newly arms the linked-worktree routing probe) and the
speculative fetch now shares create's per-remote fetch queue, as it always has
on native platforms.

Also collapse the three byte-equivalent copies of `hasLocalWorktreeBaseRef`
(create, prefetch, remote-repo create) into one in
git/worktree-base-ref-probe.ts, drop the host-only `hasLocalCommitObject` that
caused the routing bug, and add the first routing assertions on the create-path
consumers of the now-shared probe.

src/main/git/commit-object-ref.test.ts

@@ -1,22 +1,7 @@
-import { beforeEach, describe, expect, it, vi } from 'vitest'
-
-const gitExecFileAsyncMock = vi.hoisted(() => vi.fn())
-
-vi.mock('./runner', () => ({
-  gitExecFileAsync: gitExecFileAsyncMock
-}))
-
-import {
-  hasCommitObjectViaGitExec,
-  hasLocalCommitObject,
-  isFullGitObjectId
-} from './commit-object-ref'
+import { describe, expect, it, vi } from 'vitest'
+import { hasCommitObjectViaGitExec, isFullGitObjectId } from './commit-object-ref'
 
 describe('commit object refs', () => {
-  beforeEach(() => {
-    gitExecFileAsyncMock.mockReset()
-  })
-
   it('recognizes only complete git object IDs', () => {
     expect(isFullGitObjectId('a'.repeat(40))).toBe(true)
     expect(isFullGitObjectId('A'.repeat(40))).toBe(true)
@@ -49,15 +34,4 @@ describe('commit object refs', () => {
 
     expect(gitExec).not.toHaveBeenCalled()
   })
-
-  it('checks local commit objects in the target repo path', async () => {
-    gitExecFileAsyncMock.mockResolvedValue({ stdout: 'a'.repeat(40), stderr: '' })
-
-    await expect(hasLocalCommitObject('/repo', 'a'.repeat(40))).resolves.toBe(true)
-
-    expect(gitExecFileAsyncMock).toHaveBeenCalledWith(
-      ['rev-parse', '--verify', '--quiet', `${'a'.repeat(40)}^{commit}`],
-      { cwd: '/repo' }
-    )
-  })
 })