docs: 文档/配置/测试同步 NAS :8124 生产现状，清除 Node.js 与甲骨文残留

背景：文档停在 Node.js 时代或甲骨文 8123 部署，与生产（NAS :8124 + Flask +
auth-hub + ai-gateway）严重脱节，曾导致凭旧记忆误判'无线上环境'。

- CLAUDE.md 重写：技术栈/结构/命令/部署事实/关键坑（F7 button、UTC 日期、
  429 退避以 DB 为准、迁移幂等、AI 生成耗时）
- docs/ARCHITECTURE.md 重写为 Flask 蓝图+services+可插拔数据层 + NAS 部署
- docs/DEVELOPMENT.md 重写为 Flask/CRA 开发指南 + push.sh 部署流程
- docs/REQUIREMENTS.md：部署条目改 NAS 8124；补 auth-hub/AI 教练/新修复
- docs/AUTH_HUB_INTEGRATION.md 新增（补 .env.example 悬空引用）
- README.md：技术栈/DB/auth-hub/API 清单/部署节修正
- backend/config.py 与 .env.example：AUTH_HUB_REDIRECT_URI 默认 8123→8124，
  MariaDB 注释 Oracle→NAS
- tests：GatewayCourtesy 并发测试对齐 MAX_CONCURRENT(AI_JOB_CONCURRENCY=2)；
  conftest 禁用 create_app 后台队列线程，修整库测试 flaky（585 passed）

backend/tests/test_coach.py

@@ -1076,15 +1076,20 @@ class TestHighlightsReadAlone:
 
 
 class TestGatewayCourtesy:
-    """The gateway runs one worker with four threads and is shared with two
-    other projects. This consumer must not be able to saturate it."""
+    """The gateway is shared with two other projects, so this consumer must
+    not saturate it. The cap is MAX_CONCURRENT (AI_JOB_CONCURRENCY; default 2
+    since 2026-09-01) and is counted across the whole deployment, not per
+    Gunicorn worker."""
 
-    def test_only_one_job_runs_at_a_time_across_the_deployment(self, db, user):
-        jobs.enqueue(user["id"], "health", "a")
-        jobs.enqueue(user["id"], "sleep", "b")
-        assert jobs._claim_next() is not None
-        assert jobs._claim_next() is None, \
-            "a second Gunicorn worker must not start a second gateway call"
+    def test_concurrency_is_capped_at_MAX_CONCURRENT(self, db, user):
+        """More than the cap may queue, but only MAX_CONCURRENT run at once."""
+        limit = jobs.MAX_CONCURRENT
+        for i in range(limit + 2):
+            jobs.enqueue(user["id"], "health", f"job-{i}")
+        claimed = [jobs._claim_next() for _ in range(limit + 1)]
+        assert sum(1 for c in claimed if c is not None) == limit
+        assert claimed[limit] is None, \
+            "a second claim past MAX_CONCURRENT must not start another gateway call"
 
     def test_a_finished_job_frees_the_slot(self, db, user):
         jobs.enqueue(user["id"], "health", "a")