refactor: 移除 Python 后端源码，全面迁移至 Rust gateway 架构

- 删除全部 Python 源码 (src/) 及 Alembic 迁移脚本，归档至 _deprecated_py_src/
- 重构 Rust gateway ai_pipeline: 拆分 planner/finalize 模块，新增 contracts/adaptation 层
- 重组 handlers 模块为 admin/public/proxy/internal/shared 子模块结构
- 新增 executor 模块，引入 Rust 原生数据库迁移 (aether-data/migrations)
- 简化 CI/Docker 构建流程，移除 base image 二级构建，统一为单一 app image
- 移除 Python 相关基础设施文件 (entrypoint.sh, gunicorn_conf.py, Dockerfile.base)

_deprecated_py_src/core/metrics.py

@@ -0,0 +1,109 @@
+"""
+Prometheus metrics for monitoring
+"""
+
+from prometheus_client import Counter, Gauge, Histogram
+
+# 并发槽位占用时长分布（按异常类型聚合，不按 key_id 拆分）
+concurrency_slot_duration_seconds = Histogram(
+    "concurrency_slot_duration_seconds",
+    "Duration of concurrency slot occupation in seconds",
+    ["exception"],
+    buckets=[0.1, 0.5, 1, 5, 10, 30, 60, 120, 300, 600],  # 0.1s 到 10 分钟
+)
+
+# 并发槽位释放计数
+concurrency_slot_release_total = Counter(
+    "concurrency_slot_release_total",
+    "Total number of concurrency slot releases",
+    ["exception"],
+)
+
+# 请求总数（按类型）
+request_total = Counter(
+    "request_total",
+    "Total number of requests",
+    ["type", "status"],  # type values: streaming/non-streaming, status: success/error
+)
+
+# 调度：并发拒绝计数（RPM guard）
+scheduler_concurrency_denied_total = Counter(
+    "scheduler_concurrency_denied_total",
+    "Total number of candidates skipped due to concurrency/RPM limits",
+    ["is_cached_user", "reason", "reservation_phase"],
+)
+
+# 健康监控相关
+health_open_circuits = Gauge(
+    "health_open_circuits",
+    "Number of provider keys currently in circuit breaker open state",
+)
+
+# 模型映射解析相关
+model_mapping_resolution_total = Counter(
+    "model_mapping_resolution_total",
+    "Total number of model mapping resolutions",
+    ["method", "cache_hit"],
+    # method: direct_match, provider_model_name, mapping, not_found
+    # cache_hit: true, false
+)
+
+model_mapping_resolution_duration_seconds = Histogram(
+    "model_mapping_resolution_duration_seconds",
+    "Duration of model mapping resolution in seconds",
+    ["method"],
+    buckets=[0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0],  # 1ms 到 1s
+)
+
+model_mapping_conflict_total = Counter(
+    "model_mapping_conflict_total",
+    "Total number of mapping conflicts detected (same name maps to multiple GlobalModels)",
+)
+
+# ==================== API 格式转换 ====================
+
+format_conversion_total = Counter(
+    "format_conversion_total",
+    "Total number of format conversions",
+    ["direction", "source_format", "target_format", "status"],  # status: success/error
+)
+
+format_conversion_duration_seconds = Histogram(
+    "format_conversion_duration_seconds",
+    "Duration of format conversions in seconds",
+    ["direction", "source_format", "target_format"],
+    buckets=[0.0005, 0.001, 0.0025, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0],
+)
+
+# ==================== Billing migration / shadow billing ====================
+
+billing_requests_total = Counter(
+    "billing_requests_total",
+    "Total number of billing calculations",
+    ["engine_mode", "truth_engine"],  # low-cardinality labels
+)
+
+billing_fallback_total = Counter(
+    "billing_fallback_total",
+    "Total number of billing fallbacks to legacy engine",
+)
+
+billing_diff_exceeds_threshold_total = Counter(
+    "billing_diff_exceeds_threshold_total",
+    "Total number of shadow billing diffs exceeding threshold",
+    ["engine_mode"],
+)
+
+billing_invariant_violation_total = Counter(
+    "billing_invariant_violation_total",
+    "Total number of billing invariant violations (sum(breakdown)!=total)",
+    ["engine_mode", "truth_engine"],
+)
+
+# ==================== Antigravity ====================
+
+antigravity_degradation_total = Counter(
+    "aether_antigravity_degradation_total",
+    "Count of Antigravity signature degradation (rectification) events",
+    ["stage"],
+)