fix(make): worktree-rm no longer unregisters user/ for the main checkout

`submodule deinit` is needed before `worktree remove` (a populated user/
blocks it), but worktrees share .git/config — so deiniting inside the
worktree stripped submodule.user.url globally. After any `make worktree-rm`
the main checkout's `git submodule status` reported `-` (not initialised)
while user/ sat there fully intact, and a later `submodule update` would
have had no URL to work from. Re-register with an idempotent `submodule
init` after the removal.

Found by tearing down the post-location-override worktree.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Makefile

@@ -200,6 +200,12 @@ worktree-rm: guard-name
 	-git -C "$(WT_DIR)" submodule deinit -f user
 	git worktree remove --force "$(WT_DIR)"
 	git worktree prune
+	# The deinit above is required (a populated user/ blocks `worktree remove`),
+	# but worktrees SHARE .git/config — so it also strips submodule.user.url for
+	# the MAIN checkout, leaving `git submodule status` there showing `-` (not
+	# initialised) even though user/ is intact. Re-register it; init is
+	# idempotent and touches config only, never the working tree.
+	git submodule init
 	@echo "Removed $(WT_DIR). If feat/$(NAME) is merged, drop it: git branch -d feat/$(NAME)"
 
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