Added GET endpoints for activities

[guntejsingh27]

Implemented two GET routes: fetch all activities and fetch activity by ID.
This is the

[github-actions]

🔒 Security Scan Results

🔒 Security Scan Results
=========================

Bandit Scan Results:
-------------------
Run started:2025-09-18 15:29:16.074996

Test results:
	No issues identified.

Code scanned:
	Total lines of code: 1143
	Total lines skipped (#nosec): 0
	Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
	Total issues (by severity):
		Undefined: 0
		Low: 14
		Medium: 0
		High: 0
	Total issues (by confidence):
		Undefined: 0
		Low: 0
		Medium: 0
		High: 14
Files skipped (0):

Dependency Check Results:
-----------------------

✅ No critical security issues detected.

The code has passed all critical security checks.