fix: stop repeated allow_wallet_overflow column migration on restart

[feitianbubu]

⚠️ 提交说明 / PR Notice

当前 bool 类型的列，如果使用 default:true，
在 mysql 数据库下每次启动 migrate 都会重复报：
model/main.go:269 [rows:0] ALTER TABLE user_subscriptions MODIFY COLUMN allow_wallet_overflow boolean DEFAULT true
model/main.go:304 [rows:0] ALTER TABLE subscription_plans MODIFY COLUMN allow_wallet_overflow boolean DEFAULT true
因为 mysql 的 bool 默认值存储为 1，true 每次都会被识别为不匹配而重新 ALTER。

但如果改成 default:1，
又会造成在 postgres 数据库下每次启动 migrate 重复报：
model/main.go:304 [rows:0] ALTER TABLE subscription_plans MODIFY COLUMN allow_wallet_overflow boolean DEFAULT 1

目前无论使用哪种默认值字面量，都无法同时兼容 mysql 和 pg 数据库。
这与 #5361（allow_balance_pay）属于同一类问题。

📝 变更描述 / Description

去除 SubscriptionPlan.AllowWalletOverflow 与 UserSubscription.AllowWalletOverflow 两个字段的 gorm:"default:true" 列级默认值，改由业务层决定默认值（SubscriptionPlan.NormalizeDefaults 已将 nil 默认按 true 处理，UserSubscription 创建时也总是从套餐显式快照赋值），从根本上消除 AutoMigrate 每次启动的重复 ALTER，且更符合代码逻辑直觉。

🚀 变更类型 / Type of change

• 🐛 Bug 修复 (Bug fix)
• ✨ 新功能 (New feature)
• ⚡ 性能优化 / 重构 (Refactor)
• 📝 文档更新 (Documentation)

🔗 关联任务 / Related Issue

• 与 fix: stop repeated allow_balance_pay column migration on restart #5361 同类问题（allow_balance_pay 的重复 migrate）

✅ 提交前检查项 / Checklist

• 人工确认: 描述由人工整理撰写。
• 非重复提交: 已确认非重复（与 fix: stop repeated allow_balance_pay column migration on restart #5361 字段不同，互不重叠）。
• Bug fix 说明: 属于真实的启动期重复 DDL 噪音，非设计取舍。
• 变更理解: 已理解去除列默认值不影响既有业务（空值已在业务层兜底为 true）。
• 范围聚焦: 本 PR 仅去除上述两处列级默认值。
• 本地验证: go build ./model 通过；重启后不再出现上述重复 ALTER。
• 安全合规: 无敏感凭据，符合代码规范。

📸 运行证明 / Proof of Work

修复前，mysql 每次启动重复执行：

[rows:0] ALTER TABLE user_subscriptions MODIFY COLUMN allow_wallet_overflow boolean DEFAULT true
[rows:0] ALTER TABLE subscription_plans MODIFY COLUMN allow_wallet_overflow boolean DEFAULT true

去除 gorm:"default:true" 后，重启不再触发上述 DDL。

Summary by CodeRabbit

• Refactor
  • Updated wallet overflow configuration handling in subscription plans and user subscriptions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 047220f6-6739-453c-be66-d1ffda57a9cf

📥 Commits

Reviewing files that changed from the base of the PR and between 0229dc2 and f0ae2f0.

📒 Files selected for processing (1)

• model/subscription.go

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Walkthrough

Removes gorm:"default:true" from AllowWalletOverflow in both SubscriptionPlan and UserSubscription structs in model/subscription.go. JSON tags are unchanged; only the database-level GORM default annotation is dropped.

Changes

Remove GORM default:true from AllowWalletOverflow

Layer / File(s)	Summary
Remove GORM default tag from both subscription structs model/subscription.go	AllowWalletOverflow *bool in SubscriptionPlan and AllowWalletOverflow bool in UserSubscription both drop the gorm:"default:true" tag, retaining only json:"allow_wallet_overflow".

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

A tiny tag removed with care,
No more defaults hiding there,
gorm:"default:true" goodbye,
Two fields now bare beneath the sky,
The rabbit hops and all is fair! 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically summarizes the main change: removing GORM default configuration to fix repeated database migrations on restart.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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