docs: refresh two stale facts against their code arbiters

[argszero]

Summary

Two statements in docs/ no longer match the code that owns them. Both files self-describe as current state (architecture.md: 「本文说明现状」；plan-api-matrix.md: 「协议支持现状」), so stale numbers there are read as facts by new contributors. This PR refreshes them and — more importantly — makes each line point at its arbiter instead of retyping the value, so the next drift is visible at the point of editing.

The two errors have different provenance, which is why both are worth recording:

• docs/architecture.md — "迁移 v10" → v12. Correct when written, then went stale. The text was accurate at commit 6d87213 (git show 6d87213:src/db.rs really was SCHEMA_VERSION = 10); v11 and v12 landed afterwards (v12 = the transactions performance indexes, rant 2026-08-25T12:02:13, PR fix(perf): warm NFS sqlite with 64MB cache + transactions indexes + parallel trend (rant 2026-08-25T12:02:13) #150) and nothing pointed the doc back at the constant.
• docs/plan-api-matrix.md — "13 个模型" → 14. Wrong the moment it was written. The model deepseek-v4-flash-vision-exp was added in 2474f87 (2026-08-22 06:19); the doc text arrived in 6d87213 (2026-08-22 08:06), 1h47m later. Replaying that commit settles it — git show 6d87213:config/config.example.toml has 14 [[models]] and git show 6d87213:ui/js/data.js has 14 MODELS. So "13" matches no set that ever existed alongside that sentence; the 13-model state is 2474f87^.

The 14 figure is not my count, it is already a guarded contract in-repo: src/catalog_gate.rs pins MODEL_COUNT: usize = 14 (added by #173) and catalog_gate.rs/i18n_pack.rs run on every cargo test. The doc was contradicting a gate that had been in place since the same week.

Related Issue

Changes

• docs/architecture.md: 数据库 row — 「迁移 v10」→「幂等迁移至 v12，见 src/db.rs 的 SCHEMA_VERSION」
• docs/plan-api-matrix.md §4: 「13 个模型」→「14 个模型」，并注明真源（config/config.example.toml 的 [[models]]）与守卫（src/catalog_gate.rs 的 MODEL_COUNT）
• 涉及配置/数据结构的改动已同步示例文件 — not applicable: no config, schema, or code changed

Scope: exactly two files, both Markdown. No Rust source, no ui/, no i18n keys, no cache-bust. git diff HEAD -- . ':(exclude)docs/' is empty.

Tests

• cargo test 全部通过 — 165 passed / 0 failed

• cargo fmt --check 通过；cargo clippy --all-targets -- -D warnings 无 warning

• 新增/更新了单元测试（如适用）— not applicable for a Markdown-only change. Instead every fact asserted by the two edited lines was checked mechanically against its arbiter, with a negative control:

  Asserted by the doc	Arbiter	Result
  schema at v12	src/db.rs SCHEMA_VERSION	= 12 ✓
  catalog = 14 models	config/config.example.toml [[models]]	14 ✓
  catalog = 14 models	src/catalog_gate.rs MODEL_COUNT	= 14 ✓
  catalog = 14 models	ui/js/data.js MODELS	14 ✓
  "no longer says v10 / 13"	the edited files themselves	old strings absent ✓

  Negative control: replaying the same checks against a copy with the value perturbed fails, so the assertions are not vacuous.

Checklist

• 分支命名符合约定 — docs/refresh-stale-facts (docs/ per CONTRIBUTING.md)
• Commit message 使用 Conventional Commits 格式 — docs: refresh two stale facts against their code arbiters (bare docs: matching the repo's precedent in 6d87213 for multi-file doc changes)
• 单一职责，改动最小化 — one theme: stale current-state facts in docs/