refactor: prediction parser entry points

[adrunkhuman]

Summary

• Closes Polish: consolidate prediction parsers #247.
• Delete the dead positional parser and the separate line parser.
• Route admin prediction/result parsing through parse_prediction_lines directly.
• Update parser tests and the repo parsing guidance for the single parser contract.

Verification

• uv run pytest --tb=short
• uv run ruff check typer_bot tests
• uv run ty check typer_bot