feat: external events ingestion and normalization

[Alexcchip]

Summary

#8

Type of change

Addition of ingestion from PredictHQ and AskNews APIs as well as a normalized form that all future events should follow

• feat — new feature
• fix — bug fix
• docs — documentation only
• refactor — code change that neither fixes a bug nor adds a feature
• perf — performance improvement
• test — adding or updating tests
• chore / build / ci — tooling, deps, or pipeline changes

Changes

• ingest/normalize.py — the shared contract. NormalizedEvent validates on construction; dedupe_key = normalized title + city slug + local start date. Category is excluded from the key on purpose: the sources disagree on it, and that must not split one event into two rows.
• ingest/predicthq.py — structured listings near a point, paged by updated.gte. Requests deleted state explicitly so upstream cancellations propagate instead of inflating demand forever.
• ingest/asknews.py + ingest/textdates.py — infers events from news articles: one scoped search per city, prose date resolution ("August 28-30, 2026", "Q3 2027") with the precision achieved recorded rather than rounded, and a named reject reason for everything dropped.
• ingest/repository.py — upsert_event, source-agnostic. Resolves by (source, source_ref) before dedupe_key, because a revised start date changes the key and resolving by key first would orphan the original row. PredictHQ outranks AskNews on contested fields.
• ingest/run.py — ingest CLI, with --dry-run to fetch and print without writing.
• scripts/run_asknews.py — AskNews runner with the per-run cleaning report; replays recorded batches by default, --live calls the API.
• docs/event-extraction.md — architecture, file inventory, real run output for both sources, and how to test.
• Deps: adds httpx, promotes scikit-learn to a runtime dependency.
• Schema: events (one merged row per occurrence) and event_observations (append-only, one row per source sighting, raw payload kept verbatim).

Database migrations

• Includes an Alembic migration (just migrate-create "...")
• Migration runs cleanly (just migrate) and rolls back (just migrate-down)

Checklist

• Commits follow Conventional Commits
• Lint passes (just lint) and code is formatted (just format)
• Pre-commit hooks run clean (just hooks installed)
• Updated docs / README / .env.example where relevant
• Tested locally (just dev) and verified the API at http://localhost:8000/docs

How to test

1. Look at How to test it section of docs/event-extraction.md
2. This uses API credits!
   cd backend && uv run python scripts/run_asknews.py --dry-run

Notes for reviewers

At the end I added a .commit() to DB to test but this should be removed when we move to an API

Check to see if the normalized form is going to fit what we need