docs: final CST-agent → Hermit migration notice (0.10.1)

Point readers at WHC/Hermit as canonical; add MIGRATION.md and
migrate_remote_to_hermit.sh so existing checkouts can retarget origin.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/migrate_remote_to_hermit.sh

@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+# Retarget this checkout's origin to the Hermit repo (canonical name).
+# Safe to rerun. Does not rewrite history.
+#
+#   ./scripts/migrate_remote_to_hermit.sh
+#   HERMIT_REMOTE_URL=… ./scripts/migrate_remote_to_hermit.sh
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+
+NEW_URL="${HERMIT_REMOTE_URL:-https://git.whcself.xyz/WHC/Hermit.git}"
+OLD_HINT="CST-agent"
+
+if [[ ! -d .git ]]; then
+  echo "not a git checkout: $ROOT" >&2
+  exit 1
+fi
+
+cur="$(git remote get-url origin 2>/dev/null || true)"
+echo "==> current origin: ${cur:-"(none)"}"
+echo "==> target origin:  $NEW_URL"
+
+if [[ -n "$cur" && "$cur" == "$NEW_URL" ]]; then
+  echo "already on Hermit remote"
+else
+  if git remote get-url origin >/dev/null 2>&1; then
+    git remote set-url origin "$NEW_URL"
+  else
+    git remote add origin "$NEW_URL"
+  fi
+  # Keep a pointer at the old name for a while.
+  if ! git remote get-url cst-agent >/dev/null 2>&1; then
+    if [[ -n "$cur" && "$cur" == *"$OLD_HINT"* ]]; then
+      git remote add cst-agent "$cur" || true
+      echo "==> saved previous URL as remote 'cst-agent'"
+    else
+      git remote add cst-agent "https://git.whcself.xyz/WHC/CST-agent.git" || true
+    fi
+  fi
+fi
+
+git fetch origin
+branch="$(git rev-parse --abbrev-ref HEAD)"
+if git show-ref --verify --quiet "refs/remotes/origin/$branch"; then
+  git branch --set-upstream-to="origin/$branch" "$branch" 2>/dev/null || true
+fi
+
+echo
+echo "OK. Canonical repo: $NEW_URL"
+echo "  git remote -v"
+echo "  See MIGRATION.md for config / binary / env notes."
+git remote -v