tools/epro2: add Relations layer for cross-object navigation

在 replay 的扁平 objects[id] -> payload 之上盖一层 Relations，建索引和
反向引用，把孤立对象拼成可遍历的图，是后续 EPRO2 → KiCad 转换器的
中间表示前置。

Relations.build(doc) 单遍扫所有对象，得到：

主集合（按类型分桶）：
  parts / components / pins / pads / wires / nets / layers / rules

复合 ID 解析（关键）：
  '["LAYER",1]'                          → layers[1]
  '["NET","GND"]'                        → nets["GND"]
  '["PAD_NET","e0","1","e7"]'            → pad_nets_by_pad/by_net
  '["RULE","SAFE","copperThickness1oz"]' → rules[("RULE","SAFE",...)]

反向引用：
  obj_ids_by_part         partId            → 引用对象 ids（lib 内 RECT/TEXT/PIN 都带 partId）
  components_by_part      partId            → component ids
  attrs_by_parent         parentId          → ATTR ids
  lines_by_wire           WIRE.id           → LINE ids（wire 由若干 LINE 段组成）
  pad_nets_by_pad         PAD.id            → PAD_NET 记录
  pad_nets_by_net         net name          → PAD_NET 记录
  objects_on_layer / objects_in_net  字段反查

便捷 accessor：
  attrs_dict(parent_id)   折叠所有 ATTR ops 到 {key: value} dict（last
                          write wins），KiCad 转换时按 component 拿
                          Designator/Value/Footprint 的常用入口

ATTR.parentId 解析（实测发现的两种坑）：
1. 不仅指向 COMPONENT/PART —— 也大量指向 WIRE（schematic 上的网络
   标签 / 网络属性）。原查重函数漏算，636 个 false positive
   unresolved；改为"任意 doc.objects[parentId] 命中即算 resolved"
2. 复合形式 `<comp_id>-<pin_id>` 用于把 ATTR 挂在某 component 的某个
   pin 上（如 PinName）。`_resolve_parent()` 用 split("-",1) 兜底

CLI 加 --relations，按 docType 聚合 stats：
  uv run python -m tools.epro2 data/raw/oshwhub/<uuid> --relations

ESP-VoCat 验证：
  SCH_PAGE 9 docs : 572 components, 563 wires, 934 lines_grouped,
                    4111 attrs_attached, 0 unresolved_parents
  PCB      6 docs : 206 components, 807 pad_nets, 173 nets, 544 layers
  SYMBOL 105 docs : 106 parts, 560 pins, 1680 attrs_attached
  FOOTPRINT 55 docs: 496 pads, 9 nets, 1771 layers, 140 rules

注：PCB 内 pads=6 vs pad_nets=807 不矛盾 —— PAD 实例存在 FOOTPRINT
文档里，PCB stream 用 ["PAD_NET",comp,pin,pad] 复合 id 跨文档引用；
解析"comp 的某 pin 通过哪个 footprint 的哪个 pad"需要 project-级
Relations 聚合（下个 task）。

测试：tools/epro2/tests/test_relations.py 9 个单测覆盖复合 id 解析、
lineGroup 链接、parentId 直/复合解析、partId 反查、attrs 折叠。
parser + relations 共 15/15 通过。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tools/epro2/__main__.py

@@ -16,6 +16,7 @@ import sys
 from collections import Counter
 from pathlib import Path
 
+from .relations import Relations
 from .replay import Project, replay_project
 
 
@@ -71,6 +72,46 @@ def _dump_doc(proj: Project, doc_uuid: str, n_objects: int = 5) -> None:
             print(f"  {k}  →  {json.dumps(v, ensure_ascii=False)[:240]}")
 
 
+def _print_relations(proj: Project) -> None:
+    """Per-doc Relations summary aggregated across the project."""
+    print()
+    print("=" * 72)
+    print("Relations (per docType, summed)")
+    print("-" * 72)
+
+    # group docs by docType, build relations, sum stats
+    aggregated: dict[str, Counter[str]] = {}
+    samples: dict[str, str] = {}  # docType → first doc_uuid (for --dump-relations)
+    for d in proj.documents.values():
+        rel = Relations.build(d)
+        agg = aggregated.setdefault(d.doc_type or "?", Counter())
+        for k, v in rel.summary().items():
+            agg[k] += v
+        samples.setdefault(d.doc_type or "?", d.doc_uuid)
+
+    if not aggregated:
+        print("  (no documents)")
+        return
+
+    # ordered by doc count desc
+    order = sorted(
+        aggregated,
+        key=lambda t: -sum(1 for d in proj.documents.values() if (d.doc_type or "?") == t),
+    )
+    cols = [
+        "parts", "components", "pins", "pads", "wires", "nets", "layers", "rules",
+        "lines_grouped", "attrs_attached", "pad_nets",
+        "unresolved_parents", "unresolved_wires", "unresolved_layers",
+    ]
+    print(f"  {'docType':<12s}  " + "  ".join(f"{c:>16s}" for c in cols))
+    for t in order:
+        row = aggregated[t]
+        print(
+            f"  {t:<12s}  "
+            + "  ".join(f"{row.get(c, 0):>16d}" for c in cols)
+        )
+
+
 def main(argv: list[str] | None = None) -> int:
     ap = argparse.ArgumentParser(description="Replay an EPRO2 project and summarize.")
     ap.add_argument("project_dir", type=Path, help="data/raw/oshwhub/<project_uuid>/")
@@ -80,12 +121,19 @@ def main(argv: list[str] | None = None) -> int:
         default=[],
         help="dump replayed state of one document (uuid or unique prefix); repeatable",
     )
+    ap.add_argument(
+        "--relations",
+        action="store_true",
+        help="build cross-object indices and print per-docType summary",
+    )
     args = ap.parse_args(argv)
 
     proj = replay_project(args.project_dir)
     _print_summary(proj)
     for doc_id in args.dump_doc:
         _dump_doc(proj, doc_id)
+    if args.relations:
+        _print_relations(proj)
     return 0