`branchColorPatterns`: allow overlapping regexes by making evaluation order consistent

### Description

I tried to setup a detailed branch coloring for my projects, which led me to trying overlapping regexes.

But when a branch name matches **more than one** pattern, which pattern "wins" is non-deterministic, the same branch shows different colors across renders/restarts.

Example config:
```yaml
gui:
branchColorPatterns:
'^task/JT-\d+.*': 'green' # task branches of my team
'^task/.*': 'blue' # other task branches
```

Branch `task/XY-456-other` matches only the second -> consistently blue.

Branch `task/JT-123-example` matches **both** patterns -> I'd expect the first-listed one (green) to win
(or the last - which I also tried - but I would expect for it to be consistent).
Actual behavior is seemingly random: sometimes green, sometimes blue, it flips across renders/restarts.

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### Describe the solution you'd like

Having a well-defined precedence would be really nice for some fine-tuned branch-coloring scenarios, as shown in the example above.

### Describe alternatives you've considered

Since Go's regex engine doesn't support negative lookahead, overlapping patterns can't easily be made mutually exclusive as a workaround.

No file or test is named in the issue. Start by locating the branchColorPatterns configuration and the branch-color matching path; add a regression case for overlapping patterns and verify that the selected color remains consistent across renders and restarts.

Written by the indexing model from the issue text.