feat: add install command as second row on each plugin card

[tomdavidson]

Summary

Adds proto install --pin -c local <id> latest as a second copyable command row beneath the existing proto plugin add row on every plugin card.

Changes

scripts/build-jsonld.ts

• Added installCommand to the Plugin type
• Populated it in toPlugin: proto install --pin -c local ${id} latest
• Included it in toPluginEntry so it is emitted into plugins.jsonld

web/index.html

• Refactored makeCopyButton to accept cmd and ariaLabel directly (decoupled from plugin object)
• Extracted makeCmdRow(cmd, ariaLabel) — shared row builder used by both commands
• Renamed old makeCmdRow → makeAddRow(plugin) — wraps makeCmdRow for the add command
• Added makeInstallRow(plugin) — wraps makeCmdRow for the install command
• Added .cmd-rows wrapper (flex-direction: column; gap: 0.375rem) to group the two rows
• Updated buildCard to render both rows inside .cmd-rows

Result per card

proto plugin add jsonschema "https://tomdavidson.github.io/proto/jsonschema.toml"  [copy]
proto install --pin -c local jsonschema latest                                      [copy]