Add competition and match entity types

[rahulkeerthi]

Summary

Expand the register beyond players/teams/coaches to include competitions and matches as first-class entity types.

Motivation

Wikidata has cross-provider IDs for competitions and matches that would be valuable for data joining:

Property	Provider	Count
P7455	Transfermarkt match ID	26,624
P13664	FBref competition ID	148
P12758	Transfermarkt competition ID	13
P8735	Opta competition ID	53
P7460	Flashscore match ID	22
P13665	FBref match ID	4

The Transfermarkt match ID coverage (26K) is particularly useful -- it would let users resolve match IDs across providers the same way they resolve player IDs today.

What needs to change

Schema

• Add competition and match to the type CHECK constraint on entities
• Competition metadata: country, tier/level, format (league/cup)
• Match metadata: date, home_team_qid, away_team_qid, competition_qid

SPARQL extraction

• New queries for competition entities (Q500834 = association football league, etc.)
• New queries for match entities (if feasible at scale -- 26K is manageable)

CSV export

• New data/competitions.csv and optionally data/matches.csv
• Or add to existing tables with appropriate type column

API

• Existing endpoints should work (search/resolve/lookup already filter by type)
• May want /stats to show competition/match counts

Open questions

• Are match entities useful enough to justify the schema complexity?
• Should competitions include historical/defunct leagues?
• How to handle competition seasons (PL 2024/25 vs PL as a concept)?

Priority

Medium -- the current player/team/coach coverage is the core value. Competitions would be a nice-to-have for power users.