tools/epro2/kicad: Phase-2 lib_symbols — render symbol bodies from SYMBOL docs

Phase 1 emit的 .kicad_sch 里组件位置 + 属性都对，但 lib_symbols 是空
stub —— KiCad 渲染时每个组件显示成红色 "?"。Phase 2 把 SYMBOL 文档
里的 PART + RECT/POLY/CIRCLE/TEXT/PIN primitives 翻成 KiCad lib symbol
块，填到 lib_symbols 里，让 KiCad 显示真正的原理图符号。

新增 tools/epro2/kicad/sym_writer.py:
  write_lib_symbol(symbol_doc) → S-expr list 形如:
    (symbol "facere:<partId>"
      (pin_numbers (hide no))
      (pin_names (offset 1.016))
      (in_bom yes) (on_board yes)
      (property "Reference" "U" ...)
      (property "Value" "<title>" ...)
      (property "Footprint" "" hide)
      (property "Datasheet" "" hide)
      (symbol "<partId>_1_1"
        (rectangle ...)        ← from RECT.dotX1/Y1/dotX2/Y2
        (polyline (pts ...))   ← from POLY.points + closed → fill
        (circle ...)            ← from CIRCLE.center/radius
        (text "..." ...)        ← from TEXT.value/x/y/rotation
        (pin <type> line (at ...) (length ...) (name ...) (number ...))
                                ← from PIN + sibling ATTR ops
      ))

PIN 名字/编号/电气类型解析（这是关键数据探测点）：
  EPRO2 PIN 不直接带 number/name/type 字段；这些信息存为独立 ATTR 操作
  (parentId=<pin_id>, key="Pin Name"/"Pin Number"/"Pin Type")
  Pin Type 取值映射：IN→input, OUT→output, BIDIR→bidirectional,
  POWER_IN→power_in, POWER_OUT→power_out, NC→no_connect, ...
  默认 passive（保守）

sch_writer 集成（lib_symbols 自动填）：
  write_sch_page(doc, project_relations=pr) — 增 pr 可选参数
  内部 _build_lib_symbols(): 收集本 sheet 用到的 partIds → 通过
  ProjectRelations.parts_by_id 解析到 SYMBOL 文档 → write_lib_symbol →
  组装 (lib_symbols ...) 块；同 partId 多 SYMBOL 候选取第一个，去重
  WriteStats 增 lib_symbols_embedded / lib_symbols_missing

CLI 加 --no-lib-symbols 用于回到 Phase-1 行为（占位符调试用）。

ESP-VoCat 重导出验证：9/9 SCH_PAGE 全部 0 lib_miss
  P1_45092758.kicad_sch    wires=187 symbols=138 lib_emb=29
  codec_0b0163fa.kicad_sch wires=190 symbols=112 lib_emb=20
  Interface_b336a7c7.kicad_sch        symbols=95  lib_emb=13
  ...
  P1_408c9f4f.kicad_sch    wires=  6 symbols= 10 lib_emb= 3

测试：6 个新单测覆盖 outer wrapper / pin ATTR pull / 多形状 primitives /
sch_writer 集成路径 / 缺失 lib 计数 / no-pr 回退到 Phase 1。
合计 **39/39 通过**（parser 6 + relations 9 + project_relations 6 +
sexpr 6 + sch_writer 6 + sym_writer 6）。

下一步 Phase 3：footprint library + .kicad_pcb 导出。

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

tools/epro2/kicad/__init__.py

@@ -16,5 +16,6 @@ mm. Conversion factor ``MIL_TO_MM = 0.0254`` is applied at writer level.
 
 from .sch_writer import write_sch_page  # noqa: F401
 from .sexpr import Sym, to_sexpr  # noqa: F401
+from .sym_writer import write_lib_symbol  # noqa: F401
 
-__all__ = ["Sym", "to_sexpr", "write_sch_page"]
+__all__ = ["Sym", "to_sexpr", "write_sch_page", "write_lib_symbol"]