Use official OpenHCS logo family

[trissim]

Summary

• replace the accidental GitHub identicon with the supplied official OpenHCS logo family
• use purpose-specific horizontal, stacked, favicon, application, Windows, macOS, README, and hosted-plugin variants from one packaged brand authority
• make the stacked wordmark exactly match the symbol width and bump the patch release to 0.7.3

Focused validation

• 66 branding, website, Qt branding, and installer tests
• 37 hosted-plugin tests using the exact recorded submodule revisions
• deterministic PNG/ICO/ICNS regeneration
• wheel asset inventory and stale-identicon deletion check
• Ruff, shell syntax, workflow YAML, website build, and desktop Chromium screenshots

The full integration matrix was intentionally not rerun because this is an asset/projection correction; release packaging and deployment checks remain applicable.

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[augmentcode]

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