fix(pwd): guard truncation-branch string ops with -- for leading-dash dirs

[Frefreak]

Description

_tide_pwd's truncation branch passes path-derived values to string match, string escape, and string join without a -- separator. When a directory component starts with -, fish parses it as an option:

• string join / string match → unknown option, the length read fails, and the prompt collapses into a cascade of test: Missing argument / math: Too few arguments errors;
• worse, string escape --style=regex $trunc inside the disambiguation while loop errors once $trunc grows to e.g. -a, so the loop never advances and hangs the prompt when a same-prefix sibling exists.

The non-truncating path already guards its two string join calls with --; the five uses inside the truncation branch were missed. This adds -- before the path-derived argument in each.

Motivation and Context

Directories starting with - are legal and occur in practice (git worktrees, tools that encode an absolute path as a slug, etc.). Any such dir deep enough to trigger PWD truncation breaks the prompt; with a same-prefix sibling it hangs the shell. Same class of bug as fish-shell/fish-shell#10169 in prompt_pwd.

Closes #668

How Has This Been Tested

Added regression cases to tests/_tide_item_pwd.test.fish covering a leading-dash directory under truncation, both without and with a same-prefix sibling (the hang case). The pre-existing --has dashes case only covered a short path that never truncates, which is why this went unnoticed.

• I have tested using Linux.
• I have tested using MacOS.

Checklist

• I am ready to update the wiki accordingly.
• I have updated the tests accordingly.