Network groups for project topology, plus a GitHub reconnect fix

Network groups: on Starter and higher plans, create named network groups inside a project and choose exactly which apps can reach each other. Every project now has a dedicated Network groups tab for managing them.
On the Free plan, all apps in a project stay fully meshed automatically like before, now shown read-only in the Topology tab with a badge indicating it's a paid-plan feature.
The network topology view is now driven by real data end-to-end instead of a single hardcoded network, and self-hosted Pierrr Agents can resync their network state without a rebuild.

Fixed a bug where reconnecting an organization to a GitHub account after an initial link created a duplicate installation record, breaking the mapping between repositories and apps. Reconnecting now correctly updates the existing link instead of creating a duplicate.

Screenshots for the Network groups tab are coming once the screens ship to production.