feat(schema): add schema versioning, tracking, diff visualization, and history access

[Jess52487]

closes #637

Overview

Implements a complete schema‑versioning subsystem that:

• Persists each schema snapshot in a schema_version table (checksum‑based deduplication)
• Records granular changes in a schema_change table for every snapshot
• Provides a diff service that returns a structured list of SchemaChangeDiff objects
• Exposes REST endpoints for:
  • Capturing a new version (POST /schema/versions)
  • Listing historical versions (GET /schema/versions)
  • Fetching a specific version (GET /schema/:id)
  • Getting a diff between two versions (GET /schema/:id/diff/:previousId)

Why

• Enables auditability of schema evolution over time.
• Allows developers and operators to visualize exactly what changed between releases.
• Supports rollback planning and impact analysis.

Implementation Details

• Entities: SchemaVersion, SchemaChange
• Migration: Creates the two tables with appropriate indexes.
• DTOs: CreateSchemaVersionDto, GetSchemaDiffDto
• Services:
  • SchemaDiffService (pure diff logic)
  • SchemaTrackingService (persistence & retrieval)
• Controller: SchemaController with the above endpoints.
• Module: SchemaTrackingModule (self‑contained; not imported into AppModule).
• Tests:
  • Unit tests for SchemaTrackingService
  • E2E tests for SchemaController routes.

Verification

• Run npm test (unit + e2e) – all pass.
• Execute migration scripts against a test DB.
• Use curl or Postman to verify each endpoint returns the expected JSON payloads.

Staged Commits

1. Entities & migration – entities/*.entity.ts, migration file.
2. DTOs – dto/*.dto.ts.
3. Diff utility service – services/schema-diff.service.ts.
4. Tracking service – services/schema-tracking.service.ts.
5. Controller & routing – controllers/schema.controller.ts.
6. Module wiring – modules/schema-tracking.module.ts.
7. Unit tests – tests/schema-tracking.service.spec.ts.
8. E2E tests – tests/schema.controller.e2e-spec.ts.

Related Issue

Closes #<ISSUE‑ID> – Track schema changes over time

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You can now open the PR with the above title and description. Let me know if any tweaks are needed!