feat(pr): merge with the repository's defaults, ready, gh flags and ✓ lines for pr mutations

pr merge takes the method from the repository's default merge style
instead of always merging (D22), accepts gh's --merge, --squash and
--rebase next to -s/--method, refuses methods the repository disables,
and adds -d/--delete-branch (defaulting to the repository setting),
--auto, -t, -b, -F and -e. On a terminal it asks for the method and
branch deletion with the defaults preselected, without a picker when
the current branch has a pull request. It reports "✓ Squashed and
merged pull request alice/x#3 (title)", the deleted remote branch, and
switches off and deletes the local head branch; --json returns the
merged pull request. Merged, closed and draft pull requests are
reported before anything is asked. -s without a value points at
--squash.

pr checkout names the local branch after the head branch when that
name is free or already at the head, falling back to OWNER/BRANCH for
forks and pr/NUMBER (D13), fetches and switches quietly, reports
"✓ Checked out #1 into feat/one", and has the alias co. pr clean
reports what it deleted and that a remote branch was already gone.

pr create asks for the title and body, then "What's next?": submit,
submit as a draft, add metadata or change the branches, without the
AGit question up front or a final confirmation. It pushes an unpushed
head with --set-upstream --quiet ("✓ Pushed feat/one to origin"),
prints "✓ Created pull request alice/x#9 (title)" and the URL, and
adds --fill, --web, the alias new, the gh shorthands, and milestones
by title.

New tea pr ready [--undo]. pr close and reopen take -c/--comment,
close takes -d/--delete-branch, and both say when the pull request
already is in that state. pr edit reports "✓ Edited", takes the
singular gh reviewer flags (the plurals still work), milestones by
title and --remove-milestone. pr diff is colored and paged on a
terminal and byte-exact when piped, with --name-only, --color and
--web. Every pull request argument accepts #N, URLs and branch names
and defaults to the current branch's pull request.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/pull_clean_test.go

@@ -64,7 +64,7 @@ func TestPullCleanDeletesLocalAndRemoteBranches(t *testing.T) {
 		"rev-parse --verify refs/heads/pr/7^{commit}":    "abc123",
 		"rev-parse --verify refs/heads/main^{commit}":    "mainsha",
 		"symbolic-ref --short HEAD":                      "pr/7",
-		"switch -- main":                                 "",
+		"switch --quiet -- main":                         "",
 		"branch -D -- pr/7":                              "",
 	}}
 	deps.Git = runner
@@ -92,7 +92,7 @@ func TestPullCleanDeletesLocalAndRemoteBranches(t *testing.T) {
 	runner.calls = nil
 	require.NoError(t, Execute(context.Background(), deps, []string{"pr", "clean", "7", "--repo", "alice/project", "--no-input", "--json", "--yes"}))
 	require.Contains(t, runner.calls, "branch -D -- pr/7")
-	require.Contains(t, runner.calls, "switch -- main")
+	require.Contains(t, runner.calls, "switch --quiet -- main")
 	require.Contains(t, runner.calls, deleteRemote)
 	require.Contains(t, out.String(), `"local_branch":"pr/7"`)
 	require.Contains(t, out.String(), `"remote_deleted":true`)