docs(architecture): 完成技术验证 S1–S4，确定 FR-M2-05/06 目标值

- spikes/：Word 转 PDF（Gotenberg）、格式识别、原句坐标、DeepSeek 抽取四项验证代码与两版提示词；样本派生产物和 .env 不进 git
- tech-validation.md：完整结论。四项都可行：WPS 字体字符集要修正并改用行高调整过的字体；格式识别不需要 Docling；表格内切句待改进；抽取需第三道依据校验与规则兜底
- architecture.md：§3.5 加预处理与字体包，§3.6 证据校验改为三道，§10 回填结论
- 03 功能需求与 decisions.md（TV1）：召回 ≥ 99%、采纳准确率 ≥ 95%、页码 100%、高亮正文 ≥ 98% / 表格 ≥ 95%

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

spikes/s1-convert/fonts_used.py

@@ -0,0 +1,17 @@
+"""统计样本用到的字体（东亚字体），决定字体替换表要覆盖哪些。"""
+import collections, re, sys, zipfile, pathlib
+sys.path.insert(0, str(pathlib.Path(__file__).resolve().parent.parent))
+from common import IDS, sample_file, sniff
+tot = collections.Counter()
+for sid in IDS:
+    f = sample_file(sid)
+    if sniff(f) != "docx":
+        continue
+    with zipfile.ZipFile(f) as z:
+        xml = z.read("word/document.xml").decode("utf-8", "replace")
+        sty = z.read("word/styles.xml").decode("utf-8", "replace") if "word/styles.xml" in z.namelist() else ""
+    c = collections.Counter(re.findall(r'w:eastAsia="([^"]+)"', xml + sty))
+    c.update(re.findall(r'w:ascii="([^"]+)"', xml + sty))
+    tot.update(c)
+    print(sid, c.most_common(6))
+print("TOTAL", tot.most_common(15))