fix(scripts): prune never removes prod skills silently

install.ps1/-sh -Prune: a prod skill with no source in skills/ is
potentially lost knowledge. Now:
- interactive: ask per skill (default No)
- non-interactive: skip with warning
- -Yes/--yes: remove, but warn loudly
Also fixes WinPS 5.1 parse break: removed em-dash (UTF-8 0x94 reads as
" in cp1251) from install.ps1 — file is ASCII-clean again.
Lesson: pi-add-models got pruned because it lived only in prod, no source.

scripts/install.sh

@@ -4,10 +4,13 @@
 #   ~/.agents/skills/<name>/  (pi — native default scan path, agent-neutral namespace)
 # $CLAUDE_SKILLS_DIR overrides ONLY the claude target (for testing/CI).
 #
-# Usage: install.sh [--prune] [name...]
+# Usage: install.sh [--prune] [--yes] [name...]
 #   no args        = install all skills/* into both targets
 #   --prune        = after install, remove target/<name>/ dirs that are NOT in skills/*
 #                    (prune always scans full target, ignores name filter — global cleanup)
+#   --yes          = with --prune: remove prod-only skills without asking (still warns loudly).
+#                    Without --yes, prune asks per skill (default No) and NEVER removes silently:
+#                    a prod skill with no source in skills/ is potentially lost knowledge.
 set -euo pipefail
 
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
@@ -17,10 +20,12 @@ SRC="$ROOT/skills"
 TARGETS=("${CLAUDE_SKILLS_DIR:-$HOME/.claude/skills}" "$HOME/.agents/skills")
 
 prune=0
+yes=0
 positional=()
 for arg in "$@"; do
   case "$arg" in
     --prune) prune=1 ;;
+    --yes) yes=1 ;;
     *) positional+=("$arg") ;;
   esac
 done
@@ -62,13 +67,29 @@ for target in "${TARGETS[@]}"; do
 done
 
 if [ "$prune" -eq 1 ]; then
+  interactive=1
+  if [ ! -t 0 ]; then interactive=0; fi
   for target in "${TARGETS[@]}"; do
     for d in "$target"/*/; do
       [ -d "$d" ] || continue
       name="$(basename "$d")"
       if [ ! -d "$SRC/$name" ]; then
-        echo "pruning: $name (not in skills/) → $d"
-        rm -rf "$d"
+        if [ "$yes" -eq 1 ]; then
+          echo "WARN: prune: $name (not in skills/) — REMOVED from $d" >&2
+          rm -rf "$d"
+        elif [ "$interactive" -eq 1 ]; then
+          echo "WARN: prune: $name is in prod but has NO source in skills/ — possibly lost knowledge." >&2
+          printf '  Remove "%s"? [y/N] ' "$name"
+          read -r ans
+          if [ "$ans" = "y" ] || [ "$ans" = "Y" ]; then
+            rm -rf "$d"
+            echo "removed: $name"
+          else
+            echo "kept: $name (remove manually, or add it to skills/)"
+          fi
+        else
+          echo "WARN: prune skipped: $name (prod skill without source; non-interactive — nothing removed)" >&2
+        fi
       fi
     done
   done