Extend securities filters to also include short positions

[financelurker]

This change allows the "view securities" command to also show short positions in your repository.

I know, short positions in Portfolio Performance are a bit wonky, but still used by many people.

snapshot.shares now returns also negative amounts; view securities is adapted, values()/VAP/share-sell are out of scope and can be inplausible (needs a separate change).

[financelurker]

Not quite sure how to solve the build issue... Poetry gives me errors (wants to install packages in the system, despite having a venv in the repository) and make does not work either (selinux errors, I am on Fedora)...

(I have installed it as editable source-module, and this way it works...)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ma4nn]

@financelurker thanks, I have consolidated the new tests into the existing ones and build now works fine 👍

The only thing I am still struggling is:
PortfolioSnapshot.shares is consumed by several callers beyond view securities. The switch from > 0 to != 0 means shorts now flow into:

1. commands/simulate_share_sell.py:70 — holdings = snapshot.shares then iterates and runs FIFO. A short position would now be iterated and fed into enrich_fifo_lots; likely to misbehave or hit sell_strategy.py:44's clip(lower=0, ...). Needs either an explicit filter at the call site or a regression test.
2. domain/vap.py:73,141 — _calculate_min_shares clamps via max(0, …) so shorts collapse to 0 effective. Probably fine, but worth one assertion.
3. snapshot.values — now produces negative balances for shorts; any aggregate using it gets reduced by the short's market value. Intentional?

What's your take on these points?

[ma4nn]

@financelurker any thoughts on this ☝️?