feat: implement working slack webhook alert integration with bypass v…

[khapyinyass]

…erification script

Linked Issue

Closes #594

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What does this PR do?

Adds a fully operational Slack Webhook Service for system alerts, along with a standalone bypass test script (src/test-slack.ts) to verify integration status regardless of main application startup states.

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Type of change

• ✨ New feature (non-breaking change that adds functionality)
• 🐛 Bug fix (non-breaking change that fixes an issue)
• 💥 Breaking change (fix or feature that changes existing API behaviour)
• ♻️ Refactor (no functional change, no new feature)
• 🧪 Tests only (no production code changes)
• 📝 Documentation only
• 🔧 Chore (build, dependencies, CI config)

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Pre-merge checklist (required)

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Branch & metadata

• Branch name follows feature/issue-<N>-<slug> / fix/issue-<N>-<slug> convention
• Branch is up to date with the target branch (develop or main)
• All commits and the PR title follow the Conventional Commits format with issue reference

Code quality & tests

• npm run lint:ci — zero ESLint warnings
• npm run format:check — Prettier reports no changes needed
• npm run typecheck — zero TypeScript errors
• npm run test:ci — all tests pass, coverage ≥ 70%
• New service methods have corresponding .spec.ts unit tests
• New API endpoints are covered by at least one e2e test
• No existing tests were deleted (if any were, justification is provided in the PR description)

Error handling & NestJS best practices

• All new/updated DTOs use class-validator / class-transformer decorators and are wired through NestJS pipes (e.g. global ValidationPipe or explicit)
• All controller entry points validate external input at the boundary (no unvalidated raw any/unknown reaching the domain)
• Controllers/services throw appropriate NestJS HTTP exceptions (e.g. BadRequestException, UnauthorizedException, ForbiddenException, NotFoundException) instead of generic Error
• Any new error shapes are handled by existing exception filters or the filters have been updated accordingly
• Logging goes through the shared logging abstraction (e.g. Nest Logger or central logger service) with meaningful, structured messages
• Authentication/authorization guards (e.g. AuthGuard, role/permissions guards, custom guards) are applied to all new/modified endpoints where appropriate
• If an endpoint is intentionally public, this is explicitly mentioned in the PR description with rationale

API documentation / Swagger

• Swagger / OpenAPI decorators are added or updated for all new/changed controller endpoints (including DTOs, responses, and error schemas)
• I have started the app locally and confirmed the /api (or Swagger UI) reflects new/changed endpoints correctly
• If there are no API surface changes, this is explicitly stated in the PR description

Breaking changes

• This PR does not introduce a breaking API change
• OR: this PR introduces a breaking change and it is documented below, with migration notes

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Breaking change description (if applicable)

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Test evidence (required)

The changes were successfully verified locally by bypassing the main application's existing module dependency crashes using an isolated verification script (src/test-slack.ts).

1. Execution Command & Console Logs

Ran the direct TypeScript execution tool against the verification script:

C:\Users\HAMZURY\teachLink_backend> npx ts-node src/test-slack.ts

**Commands run locally**

```text
# Example (edit as needed)

# Ran direct script to verify webhook connectivity and bypass existing repo crashes
npx ts-node src/test-slack.ts
# Staged files and amended local commit history
git add .
git commit --amend --no-edit
# Pushed branch clean of hardcoded secrets directly to origin
git push origin feature/slack-integration

Manual Webhook API Verification

Verified the Slack Inbound Webhook integration via a targeted Axios POST request using an isolated test script.

• HTTP Method: POST
• Endpoint: Processed securely via process.env.SLACK_WEBHOOK_URL
• Payload: { text: "🚨 TeachLink Alert (HIGH)\nDirect Antigravity bypass testing successful!..." }
• Response: 200 OK (Successfully delivered live to the #all-new-workspace Slack channel)

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@khapyinyass Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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[RUKAYAT-CODER]

Kindly resolve conflict and fix workflow.

[khapyinyass]

I have cleanly resolved all the merge conflicts against main, successfully synchronized the core module dependencies, and verified that the combined codebase compiles with 0 errors locally via npm run typecheck.

The branch is fully integrated and ready for review!