fix(fish): preserve Darwin Homebrew path precedence over /usr/local/bin

[mederic-hurier-partner]

Summary

On Darwin, ensure /opt/homebrew/bin and /opt/homebrew/sbin take precedence over /usr/local/bin and /usr/local/sbin.

Context & Changes

• In dot_config/fish/conf.d/paths.fish, /usr/local/bin previously used -mg (--move), causing it to be shifted ahead of Homebrew paths (/opt/homebrew/bin only used -g). On Apple Silicon, this inverted tool precedence and triggered mise doctor PATH warnings.
• Switched /opt/homebrew/bin to -mg and /usr/local/bin to -g so that mise shims, ~/.local/bin, and Homebrew retain precedence over fallback binaries in /usr/local/bin.
• Added test_fish_paths_precedence_on_darwin to dot/tests/test_fish.py to prevent regressions.

Test Plan

• mise run test: 1448 passed, 3 skipped, 30 subtests passed.
• mise run check:local and check:network: all linters, formatting, and security scans passed.
• Verified path precedence in login Fish shell: mise shims (1), ~/.local/bin (2), /opt/homebrew/bin (3), /usr/local/bin (5).