fix(install): handle missing provider manifests and skills dir

With the marketplace architecture, provider-manifest.sh files and the
.agents/skills/ source directory may not exist. Guard both loops so
install.sh doesn't hard-fail when they're absent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/install.sh

@@ -8,6 +8,7 @@ source "$REPO_ROOT/scripts/deploy-manifest.sh"
 # Collect provider skill adapters from all provider-manifest.sh files
 SKILL_ADAPTERS=()
 for provider_manifest in "$REPO_ROOT"/providers/*/provider-manifest.sh; do
+  [[ -f "$provider_manifest" ]] || continue
   # shellcheck source=/dev/null
   source "$provider_manifest"
 done
@@ -35,13 +36,19 @@ for entry in "${DEPLOY_DIRS[@]}"; do
 done
 
 # Deploy skills to canonical location — merge per-skill, never wipe the parent
+# Skipped when source does not exist (marketplace architecture: skills installed via plugin)
 skills_dest="$HOME/$DEPLOY_SKILLS_SRC"
-mkdir -p "$skills_dest"
+skills_deployed=()
-for skill_dir in "$REPO_ROOT/$DEPLOY_SKILLS_SRC"/*/; do
+if [[ -d "$REPO_ROOT/$DEPLOY_SKILLS_SRC" ]]; then
+  mkdir -p "$skills_dest"
+  for skill_dir in "$REPO_ROOT/$DEPLOY_SKILLS_SRC"/*/; do
+    [[ -d "$skill_dir" ]] || continue
     skill_name="$(basename "$skill_dir")"
     rm -rf "${skills_dest:?}/${skill_name:?}"
     cp -r "$skill_dir" "$skills_dest/$skill_name"
-done
+    skills_deployed+=("$skill_name")
+  done
+fi
 
 # Create provider skill adapters as symlinks to the canonical skills location
 for adapter in "${SKILL_ADAPTERS[@]}"; do
@@ -63,7 +70,9 @@ done
 for entry in "${DEPLOY_DIRS[@]}"; do
   echo "  ~/${entry##*:}/"
 done
-echo "  ~/$DEPLOY_SKILLS_SRC/ (skills)"
+if [[ ${#skills_deployed[@]} -gt 0 ]]; then
+  echo "  ~/$DEPLOY_SKILLS_SRC/ (skills: ${skills_deployed[*]})"
+fi
 for adapter in "${SKILL_ADAPTERS[@]}"; do
   echo "  ~/$adapter -> ~/$DEPLOY_SKILLS_SRC (symlink)"
 done