Add api/sessions for SessionsTable.tsx to fetch from.

[RileyTripcony]

Add api/sessions.py

Updated app.py with new blueprint for sessions.py.

Updated models/activity.py and api/activity.py to include coach as a field.

[github-actions]

🔒 Security Scan Results

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

Bandit Scan Results:
-------------------
Run started:2025-08-24 08:16:07.493487

Test results:
	No issues identified.

Code scanned:
	Total lines of code: 1070
	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.