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/validation_test.go

@@ -106,11 +106,9 @@ func TestUsageErrorsPrecedeRequests(t *testing.T) {
 		{[]string{"pr", "attachment", "download", "1", "1", "--json"}, "attachment downloads are binary"},
 		{[]string{"pr", "attachment", "download", "1", "1", "--output-file", "-", "--json=id"}, "attachment downloads are binary"},
 		{[]string{"pr", "checkout", "7", "--detach", "--branch", "name"}, "--detach and --branch/--update are mutually exclusive"},
-		{[]string{"pr", "create", "--milestone=-1"}, "--milestone must be a positive ID, or 0 for none"},
+		{[]string{"pr", "create", "--milestone=-1"}, "--milestone must be a milestone title or a positive ID"},
 		{[]string{"pr", "create", "--assignee", "alice, "}, "assignee names cannot be empty"},
 		{[]string{"pr", "create", "--label", "bug, "}, "label names cannot be empty"},
-		{[]string{"pr", "create", "--milestone-name="}, "--milestone-name cannot be empty"},
-		{[]string{"pr", "create", "--milestone-name=Release", "--milestone=1"}, "--milestone and --milestone-name are mutually exclusive"},
 		{[]string{"pr", "create", "--agit", "--json", "--title", "x", "--no-input"}, "--json/--jq cannot be combined with --agit"},
 		{[]string{"pr", "create", "--topic", "x", "--title", "x", "--no-input"}, "--topic requires --agit"},
 		{[]string{"pr", "create", "--reviewer", "bob, "}, "reviewer names cannot be empty"},
@@ -120,8 +118,9 @@ func TestUsageErrorsPrecedeRequests(t *testing.T) {
 		{[]string{"pr", "create", "--agit", "--remote", "origin", "--reviewer-team", "core"}, "--reviewer-team cannot be combined with --agit"},
 		{[]string{"pr", "create", "--agit", "--remote", "origin", "--attachment", "log.txt"}, "--attachment cannot be combined with --agit"},
 		{[]string{"pr", "create", "--attachment", "."}, ". is not a regular file"},
-		{[]string{"pr", "edit", "7"}, "supply an edit flag"},
-		{[]string{"pr", "edit", "7", "--remove-assignees="}, "supply an edit flag"},
+		{[]string{"pr", "edit", "7"}, "nothing to edit; pass a flag such as --title (see tea pr edit --help)"},
+		{[]string{"pr", "edit", "7", "--remove-assignees="}, "nothing to edit"},
+		{[]string{"pr", "edit", "7", "--milestone", "1", "--remove-milestone"}, "--milestone and --remove-milestone are mutually exclusive"},
 		{[]string{"pr", "edit", "7", "--draft", "--ready"}, "--draft and --ready are mutually exclusive"},
 		{[]string{"pr", "edit", "7", "--title="}, "pull request title cannot be empty"},
 		{[]string{"pr", "edit", "7", "--base="}, "--base cannot be empty"},