[Feature request/minor bug] Allow mermaid-filter to work with Bun?

[Starwort]

I installed mermaid-filter with Bun rather than NPM (because NPM doesn't like actually working half the time), but now when I try to use mermaid-filter it cannot find mmdc, despite mmdc being in $PATH. Could you please add support for either lookup in $PATH or in specifically ~/.bun/bin?

[Starwort]

From the looks of it, this should be as simple as modifying externalTool() to also check in the same directory as mermaid-filter (or in ../bin if you prefer); this line already checks for ../.bin and could be copied down to check for ../bin as well