feat: implement Project mongoose model (#70)

[BigBen-7]

Summary

Closes #70

Implements the full Project/Campaign Mongoose schema as specified in the issue.

Changes

src/models/Project.model.js

• All required fields: title, description, category, goalAmount, raisedAmount (default 0), currency (default XLM), owner (ref User), stellarAddress, status (draft | pending | active | rejected | completed), coverImage, documents[], startDate, endDate
• timestamps: true for createdAt / updatedAt
• Indexes on status and owner

src/__tests__/project.model.test.js (new)

• 8 unit tests covering: default values, required field validation, enum rejection, all valid enum values, optional fields including subdocuments, and index registration

Test Results

PASS src/__tests__/project.model.test.js
  Project model schema
    ✓ saves with required fields and correct defaults
    ✓ rejects invalid status enum
    ✓ requires title
    ✓ requires owner
    ✓ requires goalAmount
    ✓ accepts all status enum values
    ✓ accepts optional fields
    ✓ has indexes on status and owner

Tests: 8 passed, 8 total

[ayshadogo]

LGTM

Sharp Contributor