test : added unit tests for goal-tracker.ts

[tmdeveloper007]

Closes #2863.

Summary of What Has Been Done:
Added a comprehensive test suite for the goal-tracker.ts utility module covering submitGoalWithRefresh function using mockable fetch.

Changes Made:

• Created test/goal-tracker.test.ts with 10 test cases
• Tested successful goal creation with commits unit (calls handleSync)
• Tested successful goal creation with prs unit (calls handleSync)
• Tested successful goal creation with other units (calls loadGoals)
• Tested fetch failure returns created=false with generic error
• Tested non-ok response with custom error from JSON
• Tested non-ok response without custom error (falls back to generic message)
• Tested handleSync throwing returns created=true with partial error
• Tested loadGoals throwing returns created=true with partial error
• Tested POST payload construction

Impact it Made:
Increases test coverage and ensures goal submission handles all error cases gracefully with proper user-facing messages.

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus