v0.4.0 — Multi-account support

Breaking changes

• pyflexweb query add now requires --account <account_id>
• Database schema bumped to v6 (NOT NULL account_id on queries)
• Legacy global token migrated to __default__ placeholder account on first run

New features

• pyflexweb account add/list/remove/rename — manage multiple IBKR accounts
• Per-account token resolution (no global fallback)
• pyflexweb query list shows account column
• Migration creates placeholder account from legacy global token

Upgrade notes

1. Run pyflexweb account rename __default__ "<YourAccountName>" to name the migrated account
2. Run pyflexweb account add <account_id> --token <token> to add additional accounts
3. Associate queries with accounts: pyflexweb query add ... --account <id>