Add file exclusion via josh stored filters (v1.2.0)

New `exclude` config field per target generates .josh-filters/<name>.josh
files with josh :exclude clauses. Josh-proxy applies exclusions at the
transport layer — excluded files never appear in the subrepo.

Preflight checks that generated filter files are committed.

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

bin/josh-sync

@@ -422,6 +422,28 @@ cmd_preflight() {
     warn ".gitea/workflows/josh-sync-reverse.yml not found (optional)"
   fi
 
+  # 4. Exclude filter files
+  local has_excludes
+  has_excludes=$(echo "$JOSH_SYNC_TARGETS" | jq '[.[] | select((.exclude // []) | length > 0)] | length')
+
+  if [ "$has_excludes" -gt 0 ]; then
+    echo ""
+    echo "4. Exclude filter files"
+
+    while IFS= read -r target_name; do
+      local filter_file=".josh-filters/${target_name}.josh"
+      if [ -f "$filter_file" ]; then
+        if git ls-files --error-unmatch "$filter_file" >/dev/null 2>&1; then
+          pass "${filter_file} exists and is tracked"
+        else
+          warn "${filter_file} exists but is NOT committed — run: git add ${filter_file}"
+        fi
+      else
+        fail "${filter_file} not generated — check parse_config"
+      fi
+    done < <(echo "$JOSH_SYNC_TARGETS" | jq -r '.[] | select((.exclude // []) | length > 0) | .name')
+  fi
+
   # Summary
   echo ""
   echo "============================="