fix: expand token column size and fix composite index exceeding MySQL limit

[johnnyluo]

Summary

• Increase Token field from varchar(255) to varchar(512) to accommodate longer FCM/APNs/web push tokens
• Remove Token from the idx_vault_party composite unique index — the combined (vault_id[255], party_name[255], token[512]) with utf8mb4 encoding totals 4088 bytes, exceeding MySQL InnoDB's 3072-byte index limit
• Unique constraint is now (vault_id, party_name) with a separate regular index idx_token on the token column
• Update RegisterDevice upsert to conflict on (vault_id, party_name) and include token in DoUpdates, so re-registration with a new push token updates the existing record

Test plan

• Register a device with a token longer than 255 characters — should succeed
• Re-register the same vault+party with a new token — should update the token in place
• Verify AutoMigrate runs without error (the existing DROP INDEX idx_vault_party call handles the transition)
• Verify FindDeviceByToken and unregister operations still work correctly

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Optimized database column size constraints for improved storage efficiency.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Plan: Pro

Run ID: 675eb6b9-3078-4160-9d54-fd4a2f6c31f9

📥 Commits

Reviewing files that changed from the base of the PR and between ce9bf68 and 8c38e10.

📒 Files selected for processing (1)

• models/device.go

🚧 Files skipped from review as they are similar to previous changes (1)

• models/device.go

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Walkthrough

Adjusted GORM column type constraints in models.Device: reduced VaultId and DeviceType to varchar(64), reduced PartyName to varchar(128), and increased Token to varchar(512). All other field properties and constraints remain unchanged.

Changes

Cohort / File(s)	Summary
GORM Column Type Constraints models/device.go	Adjusted varchar constraints: VaultId and DeviceType reduced to varchar(64), PartyName reduced to varchar(128), Token increased to varchar(512). Other field properties including not null, index associations, and validation tags unchanged.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main changes: expanding the token column size and fixing a composite index that exceeded MySQL limits.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

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• Commit unit tests in branch fix/device-token-index

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