feat(install): add --force to repoint symlinks; document worktree caveat

install.sh skipped a symlink pointing at another checkout, so there was
no scripted way to take the live set over. Add a --force flag that
repoints such divergent symlinks at the invoking clone (default run still
skips, stays idempotent). Document in INSTALL.md that the plugin must be
developed in the primary clone, not a worktree, and that --force repoints.

closes #17

install.sh

@@ -12,10 +12,19 @@
 #
 # Idempotent — existing symlinks pointing to this repo are left
 # alone; existing entries that point elsewhere are reported and
-# skipped.
+# skipped. Pass --force to repoint such divergent symlinks at this
+# clone (used to take the live set over from another checkout).
 
 set -euo pipefail
 
+FORCE=0
+for arg in "$@"; do
+    case "$arg" in
+        --force) FORCE=1 ;;
+        *) echo "unknown argument: $arg (only --force is accepted)" >&2; exit 2 ;;
+    esac
+done
+
 REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 CLAUDE_SKILLS="$HOME/.claude/skills"
@@ -34,7 +43,12 @@ link_one() {
             echo "ok    $dst -> $src"
             return 0
         fi
-        echo "skip  $dst already symlinked to $existing"
+        if [ "$FORCE" -eq 1 ]; then
+            ln -sfn "$src" "$dst"
+            echo "relink $dst -> $src (was $existing)"
+            return 0
+        fi
+        echo "skip  $dst already symlinked to $existing (use --force to repoint)"
         return 0
     fi
     if [ -e "$dst" ]; then