Add comprehensive end-to-end test: ingest → compile → read

[manavgup]

Problem

Missing critical E2E test that validates the full pipeline works from source ingestion through compilation to article reading.

Requirements

Create comprehensive E2E test covering:

• URL ingest adapter
• PDF ingest adapter
• YouTube ingest adapter
• Text ingest adapter
• Compilation process
• Article reading/retrieval

Context

This is the final Phase 1 blocker. Without this test, we cannot confidently validate the core user journey works end-to-end.

Test Scenarios

1. Ingest a URL → verify source created → verify article compiled → verify article readable
2. Ingest a PDF → verify extraction → verify compilation → verify content accuracy
3. Ingest YouTube URL → verify transcript extraction → verify compilation
4. Ingest raw text → verify processing → verify compilation

Acceptance Criteria

• E2E test suite created in tests/e2e/
• All 4 ingest adapters tested
• Compilation success verified
• Article content validated
• Test runs in CI pipeline