Fix portfolio mode by adding secAccNo parameter to compactPortfolio

[maximilian-sh]

Fixes #246

The Trade Republic API now requires secAccNo in the compactPortfolio subscription. Without it the API returns an empty portfolio silently.

Changes

• Cache securitiesAccountNumber from settings() response into self._sec_acc_no
• Pass secAccNo in compact_portfolio(), fetching it lazily if not yet available
• Raise a clear error if the account number can't be retrieved

Testing

• Confirmed v0.4.6 without fix returns empty portfolio
• Confirmed this branch returns all positions correctly

[ExploracuriousAlex]

I would make this private

[maximilian-sh]

Done, renamed to _secAccNo.

[ExploracuriousAlex]

Are all these locations still relevant to try?

In my case the securities account number is stored in settings_data["securitiesAccountNumber"]

[maximilian-sh]

Good point — simplified to only use settings_data["securitiesAccountNumber"]. The other fallbacks were speculative. Same field works for me as well.

[maximilian-sh]

Looked at the code again and reworked it a bit — moved _sec_acc_no to an instance attribute in __init__ instead of class level, dropped the unused compact_portfolio_by_type, and cleaned up the variable names. Logic is the same. Also rebased on master. Hope this can get merged.