chore: add opt-in non-production database auto-seeding

[adrunkhuman]

Goal

Add an explicit non-production auto-seed option so preview/manual-test deployments can boot with a small dummy database without running the seed script manually.

This belongs in v3 because invite-based multi-server work needs repeatable preview environments for testing first-run setup, seasons, and scoring rules.

Proposed behavior

• only works when ENVIRONMENT != production
• disabled by default
• requires an explicit opt-in env var, for example SEED_TEST_DATA=true
• requires a guild/server ID env var, for example TEST_GUILD_ID
• optionally accepts a test user ID env var, for example TEST_USER_ID
• only seeds when the target database is empty
• must not reset or overwrite an existing database automatically
• must never run in production, even if env vars are accidentally set

Why

typer_bot.dev.seed_test_data is useful for manual Discord testing, but preview deployments currently need a manual shell step before the bot starts. An opt-in auto-seed path would make disposable test deployments easier while keeping production safe.

Likely areas

• typer_bot/bot.py startup/setup hook
• typer_bot/dev/seed_test_data.py
• typer_bot/utils/config.py
• README manual testing/deployment notes
• tests around empty DB vs existing DB behavior

Testing notes

• cover that auto-seed is skipped in production
• cover that auto-seed is skipped unless explicitly enabled
• cover that missing TEST_GUILD_ID fails clearly or skips with a clear log
• cover that a non-empty DB is not reset
• cover that an empty non-production DB gets seeded when all required env vars are present

Non-goals

• no production seed behavior
• no automatic DB reset
• no Discord API calls from the seed path
• no general fixture factory/config framework

[adrunkhuman]

Moved into v3.0.0 as part of the invited-server operations track.

This should make preview/manual-test deployments easier while keeping production safe. It supports testing first-run setup, seasons, and scoring rules without manual database shell steps.