stack submit reports success (push + PR creation) without actually doing either, when origin remote is an old/renamed repo name

## Environment
- gh version 2.96.0 (2026-07-02)
- gh-stack v0.1.0
- macOS/Linux (bash), two sibling repos in the same GitHub org, one hit the bug and one didn't with the exact same command sequence

## Summary
`gh stack submit` printed full success output — branches pushed, 3 PRs created, a "Stack #478" created — but none of it actually happened on GitHub. The branches were never updated on `origin`, and no PRs existed anywhere I could find them. A second repo in the same session, using the identical workflow, worked correctly.

## Repro shape
- Repo A (worked correctly): plain repo, origin is the canonical name of the repo on GitHub.
- Repo B (bug): origin remote (`git@github.com:/.git`) is an **old/renamed name** — GitHub transparently redirects `gh api repos//` and `gh repo view` to the current canonical name. The canonical repo also happens to carry stale `fork`/`parent` metadata pointing at an unrelated third repo (from some past history), though I'm not sure that part is relevant.

Steps, same in both repos:
```
gh stack init --base branchA branchB branchC # adopts 3 existing local commits, one per branch
gh stack submit
```

In Repo A, `gh stack submit` output:
```
Checking stack state...
Pushing to origin...
✓ Created PR #N1 for branchA
✓ Created PR #N2 for branchB
✓ Created PR #N3 for branchC
✓ Stack created on GitHub with 3 PRs (stack #N4)
✓ Pushed and synced 3 branches
```
...and this was **true** — `git ls-remote --heads origin` showed the branches updated, and `gh pr view N1` etc. resolved to real, correctly-based PRs.

In Repo B, `gh stack submit` printed the **exact same shape of success output** (different PR numbers), but:
- `git ls-remote --heads origin` afterward showed the three branches **unchanged** — `branchB` (the one branch that existed before `stack init`, now rewritten to a different commit locally) was still pointing at its old pre-rewrite SHA on `origin`. `branchA` and `branchC` didn't exist on `origin` at all.
- The claimed PR numbers didn't correspond to any real PR: `gh pr view ` against the repo (by its canonical resolved name, by the old renamed name, and by the stale fork-parent repo) all failed with "Could not resolve to a PullRequest". `gh pr list --head branchA` (all three variants of repo name) returned `[]`.
- A second, unmodified `gh stack submit` run reported `PR #N1 is up to date` / `✓ Stack on GitHub is up to date with 3 PRs` / `✓ Pushed and synced 3 branches` — again fully green, again not reflecting reality.

## Workaround
Plain `git push -f origin branchA branchB branchC` (outside gh-stack) worked immediately and updated `origin` correctly. Manually running `gh pr create --repo --base ... --head ...` for each of the 3 layers created real, correctly-stacked PRs. After that, `gh stack view` correctly picked up the manually-created PRs (via head-branch matching, presumably) and rendered a consistent stack — so the local stack metadata itself wasn't corrupted, only `submit`'s push+create step silently no-op'd while reporting success.

## Impact
This is a correctness/trust issue rather than a crash: there's no error, no non-zero exit code (that I checked), and no indication anything is wrong — `gh stack submit` reports the same "everything succeeded" shape whether or not it actually did anything. Anyone scripting around this or trusting the CLI output at face value would believe their PRs are live when they aren't.

## Suspected cause
Possibly a repo-resolution issue: pushing/creating against a stale resolved repo identity (following the old→canonical rename, or the stale fork/parent link) that either 404s silently or targets a repo the invoking user doesn't actually have write access to, without the tool checking the actual API response before printing ✓.

Happy to provide more repro detail/logs if useful — this was found mid-task rather than in an isolated repro, so I don't have a minimal standalone case yet, but the shape above (rename + fork-parent metadata) is the one differentiating factor I found between the working and failing repo.

Beginne am Einstiegspunkt `gh stack submit` und reproduziere den Fall eines umbenannten Ursprungs-Repositorys anhand der Befehle und `git ls-remote`-Prüfungen im Issue. Verfolge die Ergebnisse des Pushs und der PR-Erstellung durch den GitHub-Auflösungspfad und vergleiche sie mit dem kanonischen Repository und dem Fall des Arbeits-Repositorys. Als erledigt gilt die Aufgabe, wenn fehlgeschlagene Vorgänge einen Fehler zurückgeben und keine Erfolgsausgabe erzeugen können, die behauptet, Branches und PRs seien erstellt worden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.