feat(pid): pid_symbol_list and pid_symbol_insert — blocks with tags, ports and XDATA

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

engineering/pid/__init__.py

@@ -1 +1,12 @@
 """P&ID expert and reader: symbol catalogue, lines, ISA-5.1 tags, graph."""
+
+from .insert import ensure_block, ensure_layer, insert_symbol, place_symbol  # noqa: F401
+from .symbols import (  # noqa: F401
+    CATALOG_VERSION,
+    Port,
+    SymbolSpec,
+    all_specs,
+    list_symbols,
+    resolve,
+)
+from .tags import parse_tag, split_instrument_tag  # noqa: F401