Add multi-mode roadmap generation (topic/document/quiz_performance); …

[Matee-ur-Rehman]

Overview

Implements multi-mode roadmap generation per the Study Roadmap Feature Gaps task — supports document, topic, and quiz_performance generation modes on POST /generate-roadmap.

What was added
mode field on the request (document | topic | quiz_performance), dispatched to three separate generation paths in roadmap_service.py
document mode: pulls all chunks for a document_id (ownership-scoped to the authenticated user) from the shared Chroma store, extracts topics via YAKE, generates a roadmap from real document content
quiz_performance mode: reuses WeakTopicService directly (cross-module import), marks weak topics as high priority
topic mode: unchanged from the original single-mode implementation
New get_document_chunks() in embedding/chroma_store.py — direct metadata lookup (not similarity search), enforces user_id ownership so a caller can't pull another user's document by guessing a document_id
New roadmap_generator/app/utils/topic_extractor.py — YAKE-based keyword extraction, reusing quiz_generator's existing YAKE config constants
Documented all three modes' request/response formats in docs/api-contracts.md
Bugs found and fixed along the way
chroma_store.py: .env path had one extra .parent, pointing at the repo root instead of ai-ml/ — meant CHROMA_API_KEY/CHROMA_TENANT/CHROMA_DATABASE were never actually loaded from ai-ml/.env, regardless of what was set there.
weak_topic_service.py: default data file path was a bare relative string ("data/quiz_results.json"), which only worked if the process happened to be started from inside weak_topic_detection/ itself. Fixed to resolve as an absolute path anchored to the file's own location.
Testing

All three modes verified end-to-end locally with a real JWT and real Chroma Cloud data:

topic — generated a correct 4-step Algorithms roadmap
quiz_performance — generated a correct roadmap from weak-topic demo data
document — generated a correct roadmap from a real uploaded PDF's actual extracted content (verified topics matched the source document's subject matter)
Note for reviewers

Checked web/backend/routes/roadmap.py on main — it currently calls the old single-mode contract with no mode field. Per the task's Submission: line, this is expected to be Pluto's separate web/roadmap-entry-points branch updating to match this new contract, not something this PR needs to stay compatible with.

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