feat(pool,scheduling): 号池调度维度、配额冷却机制与管理后台重构

- 新增 scheduling_dimensions 模块，为每个 Key 计算多维调度状态(手动/冷却/熔断/成本/健康)
- 新增 quota_cooldown 模块，统一判定 Key 的有效冷却原因
- Pool 管理后台 API 扩展 Key 详情字段(调度状态/维度/配额/OAuth 信息)
- 前端 Pool 管理页面重写，支持调度状态展示、批量清理封禁 Key
- Handler 基类增加请求调度元数据采集，stream telemetry 增强
- 请求时间线组件增强，支持 attempted 候选展示
- Kiro OAuth 凭证导入解析改进
- 新增 usage 表 provider_key 索引迁移
- 补充调度维度、配额冷却、候选枚举等单元测试

Closes #197

Co-authored-by: AAEE86 <33052466+AAEE86@users.noreply.github.com>

alembic/versions/20260303_1000_a1b2c3d4e5f6_add_idx_usage_provider_key.py

@@ -0,0 +1,45 @@
+"""add_idx_usage_provider_key
+
+Add composite index on usage(provider_id, provider_api_key_id) to support
+the pool management page's per-key usage stats aggregation query.
+
+Revision ID: a1b2c3d4e5f6
+Revises: dd0278c0a28c
+Create Date: 2026-03-03 10:00:00.000000+00:00
+"""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "a1b2c3d4e5f6"
+down_revision = "dd0278c0a28c"
+branch_labels = None
+depends_on = None
+
+INDEX_NAME = "idx_usage_provider_key"
+TABLE = "usage"
+COLUMNS = ["provider_id", "provider_api_key_id"]
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    result = bind.execute(
+        sa.text("SELECT 1 FROM pg_indexes WHERE indexname = :name"),
+        {"name": INDEX_NAME},
+    ).fetchone()
+    if result:
+        return
+    op.create_index(INDEX_NAME, TABLE, COLUMNS)
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    result = bind.execute(
+        sa.text("SELECT 1 FROM pg_indexes WHERE indexname = :name"),
+        {"name": INDEX_NAME},
+    ).fetchone()
+    if not result:
+        return
+    op.drop_index(INDEX_NAME, table_name=TABLE)