feat(checkout): merge PR action with real-GitHub e2e test (#814)

* feat(checkout): merge PR action with real-GitHub e2e test

Adds a `checkoutPrMerge` server RPC backed by `gh pr merge` (squash, merge,
or rebase) and surfaces three new actions in the git-actions menu —
"Squash and merge", "Create a merge commit", "Rebase and merge" — with
squash taking the primary slot when a PR is open and mergeable. Also
renames the existing local merge action to "Merge locally" to disambiguate
it from the new GitHub-side merge.

Adds an end-to-end test that creates a real temporary GitHub repo, opens a
PR via the daemon, polls until mergeable, calls `checkoutPrMerge`, and
verifies the merge landed on `main` — no mocks. The test pre-flights the
`delete_repo` scope so it skips cleanly on tokens that can't tear down,
and fails loud if cleanup ever errors so we don't leak repos.

PR status gains an optional `mergeable` field (`MERGEABLE | CONFLICTING |
UNKNOWN`) populated from `gh pr view --json mergeable`. The schema is
backward compatible — old payloads without the field still parse and
default to `UNKNOWN` via `z.catch`.

* Update PR status snapshot expectations

* refactor: collect git/checkout/PR feature into packages/app/src/git/

Move 21 git/checkout/PR files out of components/, hooks/, stores/, screens/,
utils/ flat-peer slop into a single packages/app/src/git/ module with
shrunk filenames (git-diff-pane.tsx -> diff-pane.tsx, use-git-actions.ts ->
use-actions.ts, etc).

Dedupe: drop the duplicate useGitActionHandlers from diff-pane.tsx — the
shared useGitActions hook is the single source. Drop the
buildGitActionsForPane wrapper. Collapse the merge-PR triple fan-out
(mergePrSquash/Merge/RebaseStatus) into one record keyed by
CheckoutPrMergeMethod. Streamline server-side single-use helpers
(dispatchStash/PullRequestMessage adapters, GitHubPullRequestMergeError
wrapper, legacy worktree test helpers).

Schema-additive only: messages.ts exports CheckoutPrMergeMethod and
PullRequestMergeable types; daemon-client.ts uses the typed alias.
Backward-compatible.

Net delta: 43 files, +219/-1212.

* fix(app): use GitHub icon for all merge-PR menu actions

* test: namespace temp GitHub repos under `paseotmp-` and centralize naming

Old prefixes (`paseo-checkout-ship-`, `paseo-e2e-`, `paseo-checkout-pr-merge-`)
collided with the `paseo-*` namespace of real repos, making bulk cleanup
unsafe. Switch every test that creates real GitHub repos to a single
unmistakable `paseotmp-` prefix, owned by one shared helper per test
boundary so no caller can name a repo outside the namespace.

- New `packages/server/src/server/test-utils/temp-github-repo.ts` exports
  `TEMP_GITHUB_REPO_PREFIX` + `createTempGithubRepoName(category)`; both
  server e2e tests (checkout-ship, checkout-pr-merge) consume it.
- `packages/app/e2e/helpers/github-fixtures.ts` locks the prefix internally
  and now requires callers to pass a `category` instead of an arbitrary
  `prefix`. Updated pr-pane and composer-attachments specs accordingly.

packages/app/src/git/github-url.ts

@@ -0,0 +1,53 @@
+// TODO: this duplicates parseGitHubRepoFromRemote in packages/server/src/services/github-service.ts.
+// Consolidate into a shared package once we have a third caller.
+
+// Note: SSH host aliases (e.g. `git@github-work:acme/repo.git` resolved via ~/.ssh/config)
+// are not detected here, so the GitHub action will silently not appear for those remotes.
+export function parseGitHubRepoFromRemote(remoteUrl: string | null | undefined): string | null {
+  const trimmed = remoteUrl?.trim();
+  if (!trimmed) {
+    return null;
+  }
+
+  let cleaned = trimmed;
+  if (cleaned.startsWith("git@github.com:")) {
+    cleaned = cleaned.slice("git@github.com:".length);
+  } else {
+    let parsed: URL;
+    try {
+      parsed = new URL(cleaned);
+    } catch {
+      return null;
+    }
+    if (parsed.hostname !== "github.com") {
+      return null;
+    }
+    try {
+      cleaned = decodeURIComponent(parsed.pathname.replace(/^\/+/, ""));
+    } catch {
+      return null;
+    }
+  }
+
+  cleaned = cleaned.replace(/\/+$/, "");
+  if (cleaned.endsWith(".git")) {
+    cleaned = cleaned.slice(0, -".git".length);
+  }
+  if (!cleaned.includes("/")) {
+    return null;
+  }
+  return cleaned;
+}
+
+export function buildGitHubBranchTreeUrl(input: {
+  remoteUrl: string | null | undefined;
+  branch: string | null | undefined;
+}): string | null {
+  const repo = parseGitHubRepoFromRemote(input.remoteUrl);
+  const branch = input.branch?.trim();
+  if (!repo || !branch || branch === "HEAD") {
+    return null;
+  }
+  const encodedBranch = branch.split("/").map(encodeURIComponent).join("/");
+  return `https://github.com/${repo}/tree/${encodedBranch}`;
+}