feat: implement backend functionality for interview question suggestion

[Linchen-Xu]

Context

Please include a summary of the changes and the related issue. Please also include relevant motivation and context. List any dependencies that are required for this change.

Changes

Please list your changes here. For example:

• Add new tests

Screenshot (if applicated)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
app.py	114	54	53%	41–42, 49–56, 61–91, 98, 102, 107, 111, 122, 127, 129, 134, 138, 147–161, 165–202, 206
modules
evaluator.py	56	14	75%	96–97, 104–122
langgraph_qa.py	19	18	5%	2–33
parser.py	12	1	92%	20
upload.py	25	3	88%	23, 46–47
TOTAL	226	90	60%

Tests	Skipped	Failures	Errors	Time
11	0 💤	0 ❌	0 🔥	41.050s ⏱️