refactor(agents-init): use the shared repo helpers

Renames _agents_init_install_tools to _agents_repo_install_tools now that
the vault shares it, collapses the two duplicated root-symlink blocks into
one loop, and routes the auto-commit through _agents_repo_sync so a failed
rebase can no longer be committed as conflict markers.

functions/_agents_repo_install_tools.fish

@@ -0,0 +1,49 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# SYNOPSIS
+#   _agents_repo_install_tools <repo_dir>
+#
+# DESCRIPTION
+#   Copies the canonical version-bump script and git hook shims from
+#   fish-config's scripts/agents-tools/ into <repo_dir>/.agents-tools/,
+#   refreshing them when the shipped agents-tools-version: marker is newer
+#   than the installed copy. Files are made executable. Idempotent: prints
+#   nothing when the installed tooling is already current, or a short summary
+#   line when it installed or updated the tooling. Shared by agents-init and
+#   agents-vault.
+#
+# ARGUMENTS
+#   repo_dir  Absolute path to the git repo root to install tooling into
+#
+# EXIT STATUS
+#   0  Tooling is current or was installed/updated successfully
+#   1  Canonical source missing or a copy failed
+#
+# EXAMPLE
+#   set -l msg (_agents_repo_install_tools /path/to/AGENTS)
+#   test -n "$msg"; and echo $msg
+function _agents_repo_install_tools --argument-names repo_dir
+    test -n "$repo_dir"; or return 1
+    set -l src (path resolve (status dirname)/../scripts/agents-tools)
+    test -f "$src/version-bump"; or return 1
+    set -l dest "$repo_dir/.agents-tools"
+
+    set -l want (command grep -m1 -oE 'agents-tools-version: *[0-9]+' "$src/version-bump" 2>/dev/null | command grep -oE '[0-9]+$')
+    set -l have ""
+    test -f "$dest/version-bump"; and set have (command grep -m1 -oE 'agents-tools-version: *[0-9]+' "$dest/version-bump" 2>/dev/null | command grep -oE '[0-9]+$')
+
+    test "$want" = "$have"; and return 0
+
+    mkdir -p "$dest/hooks"; or return 1
+    command cp "$src/version-bump" "$dest/version-bump"; or return 1
+    command cp "$src/hooks/pre-commit" "$dest/hooks/pre-commit"; or return 1
+    command cp "$src/hooks/prepare-commit-msg" "$dest/hooks/prepare-commit-msg"; or return 1
+    chmod +x "$dest/version-bump" "$dest/hooks/pre-commit" "$dest/hooks/prepare-commit-msg"; or return 1
+
+    if test -z "$have"
+        echo "→ Installed AGENTS/.agents-tools/ (version-bump v$want)"
+    else
+        echo "→ Updated AGENTS/.agents-tools/ (v$have → v$want)"
+    end
+end