feat: persist workflow admission and initial execution graph

internal/storage/mysql/migrations/000018_workflow_wait_identity.up.sql

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+-- 冻结等待的信号身份和契约；历史NULL记录必须经固定定义核验，不能默认解释为新等待。
+ALTER TABLE weave_waits
+ ADD COLUMN signal_name VARCHAR(128) CHARACTER SET ascii COLLATE ascii_bin NULL COMMENT '冻结信号名称；TIMER及待核实历史记录为空',
+ ADD COLUMN payload_version VARCHAR(32) CHARACTER SET ascii COLLATE ascii_bin NULL COMMENT '冻结信号内容契约版本；TIMER及待核实历史记录为空',
+ MODIFY COLUMN correlation_key VARBINARY(764) NOT NULL COMMENT '精确UTF8业务关联且保留尾部空格；新受理最多512字节，兼容历史191字符最多764字节，TIMER为空串';
+
+ALTER TABLE weave_instances MODIFY COLUMN business_key VARCHAR(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_bin NULL COMMENT '精确业务追踪键，保留尾部空格，不提供业务幂等';