Repos deleted, renamed or transferred on GitHub are never pruned; a rename leaves a ghost entry and offers to clone a second copy #469

What's wrong

SyncGitHubRepoInfoForOwner (ProjectDirector/ProjectDirector.cs ~L997-1035) only ever adds or overwrites entries in Options.Repos (~L1020). Nothing removes an entry once GitHub stops returning it. The only removal in the codebase is RejectUnsupportedRepos, which handles non-GitHub repo types.

Failure scenarios

• Rename: owner/Foo is cloned at <dev>/owner/Foo and then renamed upstream to Bar. On the next Scan > GitHub Owners, owner.Bar is added with LocalPath = <dev>/owner/Bar. That path isn't cloned, so its panel offers Clone. Meanwhile the old owner.Foo entry stays, still holds the clone, and is still auto-fetched. The owner now lists both. Clicking Clone on Bar makes a second full copy of the same repo, and from then on Similar Repos and file propagation compare and propagate against both copies.
• Delete or transfer: the repo stays listed under its old owner, shows up in every Similar Repos table and as a propagation target, and Clone fails with Repository not found every time.

Suggested fix

1. After an owner's listing fully succeeds (never on an ApiException or a partial result), find the Options.Repos entries for that OwnerName that the listing didn't return.
   • Remove the ones that aren't cloned.
   • Keep the ones that are cloned, and log "<name> is no longer on GitHub (deleted, renamed or transferred); local clone at <path> kept". Optionally pair a kept clone with its renamed entry by comparing git remote get-url origin to the new CloneUrl, since GitHub redirects old URLs.
2. Clear BaseRepo/CompareRepo if either names a removed entry. ClearSelectionIfRejected can be reused for this.

Acceptance criteria

• Rescanning after an upstream delete removes the uncloned entry.
• After an upstream rename, no stale uncloned entry remains, and any cloned entry that was kept is reported in the log.
• A failed or partial listing prunes nothing.
• A test covers pruning, keeping a cloned entry, and the failed-listing case.