Replace `as any` casts with proper TypeScript types

[DeFiVC]

What

Replace as any type assertions throughout the codebase with proper TypeScript types to improve type safety and catch potential runtime errors at compile time.

Why

Using as any defeats the purpose of TypeScript's type system and can mask bugs. It also makes refactoring harder since the compiler can't verify correctness.

Affected Files

1. src/middleware/rate-limit.ts (lines 20, 54, 68, 86) - request as any
2. src/modules/admin/webhook.service.ts (lines 61, 224, 260, 271) - Untyped parameters
3. src/services/webhook-dispatcher.ts (line 160, 234) - payload as any, col: any
4. src/routes/versioning.ts (line 34) - (request as any).apiVersion
5. src/stellar/transactions.ts (line 28) - (err as any)?.response
6. src/stellar/client.ts (lines 98, 151, 184, 217, 253) - err: any
7. src/middleware/response-envelope.ts (line 13) - (request as any).apiVersion
8. src/middleware/validation.ts (lines 32, 41) - result.data as any

Scope

• Define proper interfaces/types for request objects with additional properties (e.g., apiVersion)
• Use unknown for error types and narrow with type guards
• Create proper return type interfaces for webhook stats
• No functional changes

Acceptance Criteria

• No as any casts remain in the codebase
• TypeScript compilation succeeds with strict mode
• Error handling properly narrows types before accessing properties
• All type assertions use more specific types or unknown

Technical Context

• The codebase uses Fastify with TypeScript
• Error types from Stellar SDK and HTTP calls need proper typing
• Request augmentation should use module augmentation or proper interfaces

[Yungmon22]

@Yungmon22 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi Maintainer, I’ve gone through the issue requirements and relevant documentation. I have a clear understanding of the task and am confident I can deliver a solid solution. I’d be glad to discuss my approach before I begin.

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[Cyber-Mitch]

@Cyber-Mitch has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Greetings Maintainer!
I want to work on this issue. I'll make a PR within 24 hours of assignment

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Cyber-Mitch to this issue.

[akasom-creator]

@akasom-creator has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I’d like to work on this because it’s a good cleanup that improves type safety without changing behavior. I’d trace each "as any", replace it with proper Fastify/TypeScript types or "unknown" with type guards, then run strict TypeScript checks and tests to catch any issues.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @akasom-creator to this issue.

[drips-wave]

Congratulations, @Cyber-Mitch! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@Cyber-Mitch's PR #507 was approved and merged by @DeFiVC.

🏆 @Cyber-Mitch: You earned 40 FoxPoints for this contribution! Your current tier: Builder (1,126 total points). Track your full progress on GrantFox.

👏 Great work, @Cyber-Mitch! Keep contributing to ChainLearnOfficial.

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This issue has been completed by @Cyber-Mitch as part of the Stellar Wave Program's 9th Wave 🥳

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