[plugin] Add PlugNspectr

[kmturley]

Summary

• Adds PlugNspectr, an analyzer that measures the frequency response, harmonic distortion, and dynamics of other audio plugins in your DAW in real time, by Kevin Jenkins.
• License: GPL-3.0. Windows VST3 + AU (2 bundles: Pre/Post) — macOS build still to come per upstream.
• This one caught a real dev:fetch bug: the zip triggers unzip's harmless "backslashes as path separator" warning (exit 1), which was discarding the whole archive inspection and falling back to unreliable release-note text matching (wrongly adding component/AU from a sentence about a future macOS build). Fixed in [fix] Two more dev:fetch bugs found in batch 6 #675 — this PR reflects the corrected contains: [vst3].

Test plan

• npm run dev:validate passes
• npm run check passes

[github-actions]

VirusTotal Report:

• test/downloads/kevin-jenkins/plugnspectr/1.0.1/0-PlugNspectr-1.0.1-Windows-x64.zip

[github-actions]

Destination urls:
Registry: https://open-audio-stack.github.io/open-audio-stack-registry/plugins/kevin-jenkins/plugnspectr
Site: https://studiorack.github.io/studiorack-site/plugins/kevin-jenkins/plugnspectr

[github-actions]

Plugin author notification:

@kevin-jenkins — your plugin has been submitted to the Open Audio Stack registry. Please review this PR and let us know if the metadata (name, description, tags, files) is correct. To see a full list of all currently added plugins, click here.

[kevin-jenkins]

Thanks for the add, @kmturley!