[P3] Add Swagger decorators to DonationsController

[cyber-punk112]

Description

src/donations/donations.controller.ts has no @ApiTags, @ApiOperation, @ApiOkResponse or @ApiQuery decorators at all, unlike PoolsController and AuthController which are fully documented. main.ts's Swagger DocumentBuilder also doesn't addTag('donations', ...), so both of DonationsController's endpoints (GET /pools/:id/donations, GET /users/me/donations) show up undocumented (or under a default group) in /api-docs.

Deliverables

• Add @ApiTags('donations') to DonationsController and .addTag('donations', ...) in main.ts's DocumentBuilder
• Add @ApiOperation/@ApiOkResponse/@ApiQuery decorators to findByPool and findMyDonations
• npm run build passes

[bonatkenneth-web]

@bonatkenneth-web has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello Maintainer, I’d love to work on this project. I’m a professional, experienced, and confident in my ability to contribute high-quality work.

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