fix: harden installer symlink logic and interactive sourcing

- install-claude-profiles: distinguish broken symlink vs real dir vs free
  path via -L/-e, repoint existing links with ln -sfn, warn instead of
  silently skipping when target is a non-symlink dir.
- profiles.sh: only set -euo pipefail when sourced non-interactively so
  sourcing in an interactive shell doesn't clobber session settings.

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

bin/install-claude-profiles

@@ -11,7 +11,12 @@ ALIAS_LINE="source $TARGET_REPO/shell/aliases.sh"
 mkdir -p "$TARGET_DIR"
 
 if [[ "$REPO_DIR" != "$TARGET_REPO" ]]; then
-  if [[ ! -e "$TARGET_REPO" ]]; then
+  if [[ -L "$TARGET_REPO" ]]; then
+    ln -sfn "$REPO_DIR" "$TARGET_REPO"
+  elif [[ -e "$TARGET_REPO" ]]; then
+    echo "Warning: $TARGET_REPO exists and is not a symlink;" >&2
+    echo "         aliases will point there. Remove it to repoint to $REPO_DIR." >&2
+  else
     ln -s "$REPO_DIR" "$TARGET_REPO"
   fi
 fi

lib/profiles.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
-set -euo pipefail
+# Only enforce strict mode when sourced non-interactively, so sourcing this
+# file in an interactive shell doesn't clobber the user's session settings.
+[[ $- == *i* ]] || set -euo pipefail
 
 repo_root() {
   local script_dir