docs: 在阶段 C 冻结 graph 表生成 API、索引与校验规范

[0x5143]

Motivation

• 在进入实现前需要冻结 graph 表的生成 API、内建索引约束与校验规则，以避免 parser、validator、template 与文档在后续实现中各自演进。
• 目标是确保文档、生成器与运行时行为一致，并禁止在 DataTableProcessor 主流程中追加 graph 专用分支。

Description

• 修改了 docs/optimization-plan-2026-07.md，在阶段 C（Milestone 3）新增 C4 条目以提出并冻结 graph 表规范要点。
• 在新增条目中列出需要确认的生成 API（节点集合查询、出/入/关联边查询、前驱/后继/邻居查询、两点边查询、HasEdge/HasPath、FindPath、BFS、TryGetEdge/edge id 查询）。
• 指明需要确认的索引约束（EdgeId 内建唯一索引、From/To 分组索引、节点集合是否由 From/To 自动推导）和校验规则（EdgeId/From/To 非空、EdgeId 唯一、Weight 必须可解析为数字、是否允许自环/重边/孤立节点/无向语义）。
• 增加验收标准，要求在实现前冻结 API 命名与返回类型，确保文档、parser、validator、template 行为一致，并禁止在 DataTableProcessor 主流程继续添加 graph 专用分支，且引用了 docs/graph-table-design.md 作为背景设计。

Testing

• 运行了自动检查 git diff --check，结果通过（无格式/空白错误）。
• 使用 git status --short 验证工作区状态为已提交变更。

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[chatgpt-codex-connector]

Update graph freeze task to match implemented status

The referenced design doc already says graph is implemented and lists GraphTableParser/the graph template as added (docs/graph-table-design.md lines 3 and 126-130), so adding this as work to freeze "before implementation" makes the phase plan stale as soon as it is introduced. In this context, readers following the plan would treat completed parser/template/validation work as not started; please reword this as reconciling or validating the existing graph implementation and its remaining policy gaps.

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