test : added unit tests for anthropic.ts

[tmdeveloper007]

Closes #2864.

Summary of What Has Been Done:
Added a test suite for the anthropic.ts AI summary generation module covering generateWeeklySummary function.

Changes Made:

• Created test/anthropic.test.ts with 1 test case
• Tested generateWeeklySummary returning null when ANTHROPIC_API_KEY is not set

Impact it Made:
Increases test coverage for the lib directory and ensures AI summary generation degrades gracefully when the API is unavailable.

[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