fix(mkrep): stop the test suite creating real repos, and confirm implicit ones

Two related defects on the `$GIT_SERVER` auto-create path added in #150.

The test suite was creating repositories on a live forge. mkrep resolves a
server from `$GIT_SERVER` plus `$GITEA_URL`/`$GITEA_HOST`, and this repo
doubles as a real ~/.config/fish where all of them are exported, so the six
sections that call a bare `mkrep <dir>` took the auto-create branch and
contacted the server. That is how an empty `rootiest/repo` came to exist on
git.rootiest.dev on 2026-09-14 (since deleted). It also explains why those
cases looked flaky rather than broken: standalone they passed, because the
repo existed and mkrep linked instead of creating, while under
run-tests.fish they failed with `Error: no available login` — a throwaway
XDG_CONFIG_HOME leaves `tea` with no credentials. Passing for that reason is
worse than failing.

The suite now neutralizes all five variables once at setup, the same
shadow-to-empty pattern already used per-section for --check-existing, whose
comment flagged this exact hazard. Nothing depended on the ambient value:
every section wanting a server sets its own `set -lx GIT_SERVER`, and one
section asserts the opposite outright.

mkrep itself now confirms before an implicit create. Creating a repository
on a forge is the only outward-facing thing mkrep does, and on this path an
exported variable is all it takes to reach it, so `mkrep foo` — which reads
as purely local — would make a repo on a server without saying so. It asks
first, defaulting to no; declining leaves the local repo with no remote and
still exits 0. Provenance is what gates the prompt, not the resolved value:
--server, --remote and --new-remote all state outright what they will do, so
none of them prompts, and --yes skips the question. Where it cannot be asked
(a script, a pipe, any non-interactive shell) creation is skipped rather than
assumed, with a note on stderr naming the flags that would allow it.

Nine new assertions cover the skip, its stderr note, --yes, and --server not
prompting. The interactive read is verified by hand under a PTY, both
answers, but is not in the suite: that needs a pseudo-terminal, and the
answer parsing it guards is a single `string match`.

docs/fish-config.md

@@ -1275,7 +1275,7 @@ functions). They are active in all interactive sessions.
                      [-c | --clean | --no-clean] [--strict] [-v | --verbose]
                      [-s | --silent] [--template <path>] [--branch <name>]
                      [--remote <url>] [--new-remote [<cmd>]] [--server <type>]
-                     [--check-existing] [--name <name>] [-h | --help] <dir>
+                     [--check-existing] [-y | --yes] [--name <name>] [-h | --help] <dir>
 
     Creates a directory, cds into it, and git-inits it -- mkcd plus a git
     repo in one step. All three actions are on by default and each has a
@@ -1323,6 +1323,19 @@ functions). They are active in all interactive sessions.
     requires a resolved server and is mutually exclusive with --remote
     and --new-remote.
 
+    Creating a repository on a live forge is the only outward-facing thing
+    mkrep does, and on the $GIT_SERVER path an exported variable is all it
+    takes to reach it -- so a plain mkrep call, which reads as purely
+    local, would otherwise make a repo on a server without ever saying so.
+    That case therefore asks for confirmation first, defaulting to no.
+    Declining leaves the local repo in place with no remote and still
+    exits 0. Linking an existing repo is not affected, and neither is an
+    explicitly requested remote: --server, --remote and --new-remote all
+    say outright what they are going to do, so none of them prompts. Pass
+    --yes to skip the question. Where it cannot be asked -- a script, a
+    pipe, any non-interactive shell -- creation is skipped rather than
+    assumed, with a note on stderr naming the flags that would allow it.
+
     Arguments:
       <dir>            Directory to create and enter
       --cd, --no-cd    Change into <dir> (default: --cd)
@@ -1344,12 +1357,15 @@ functions). They are active in all interactive sessions.
       --server <type>  Auto-create/link a remote on gitea, gitlab, or github
       --check-existing Report whether the repo exists on the resolved
                        server; creates or links nothing
+      -y, --yes        Create the remote without confirming, on the
+                       $GIT_SERVER path that would otherwise ask
       --name <name>    {name} substitution for --new-remote/--server
                        (default: <dir>'s basename)
       -h, --help       Show this help message
 
     Exit Status:
-      0  All requested steps completed
+      0  All requested steps completed, or a $GIT_SERVER remote-create was
+         declined at the prompt (the local repo is still set up)
       1  Bad arguments, or a step (mkdir, cd, git init, remote) failed
 
     Example:
@@ -1360,7 +1376,8 @@ functions). They are active in all interactive sessions.
     mkrep --new-remote ~/projects/foo
     set -gx GITEA_URL https://git.example.com
     set -gx GIT_SERVER gitea
-    mkrep ~/projects/foo
+    mkrep ~/projects/foo        # asks before creating the remote
+    mkrep --yes ~/projects/foo  # creates it without asking
     mkrep --server gitlab --check-existing ~/projects/foo
 
     Starting points for $MKREP_REMOTE_CMD, one per host CLI -- each assumes