fix: convert text chart in to mermaid chart

[arnoldsandoval]

Why

The navigation reference in hub/docs/gallery.md lays out Hub's main flows: creating a prototype, browsing registered branches, managing prototypes, and drilling into a prototype card. It did this as an indented plain-text tree, which GitHub renders as a raw monospaced block. I had a hard time parsing it quickly so I swapped it for a Mermaid chart. It keeps the same information in the file but renders it as a diagram, which is easier to read and easier to update when the navigation changes.

What changes

The outline section now renders as a flowchart instead of an ASCII tree. Nothing about the flows themselves changed, just the presentation:

• The diagram source is split into commented sections (Create, Prototypes list, Manage prototypes, Prototype card detail) so it's easy to find the edges you need to edit.
• The Templates catalog route uses a dashed edge to show it's an optional branch off Create, not a required step.
• The prototype card's sub-flows (review shell, branch from here, build history → build details) sit inside a Mermaid subgraph, so the card reads as one container and links cleanly from the Prototypes list.

[nshki]

Wholeheartedly agree with the Mermaid conversion. Thank you for this contribution. 🙇🏻