Planner plugin extension points

[hykilpikonna]

The current plugin system supports isolated plugin UI, routes, plugin-owned data, and read-only access to core entities. To move the features on my https://github.com/hykilpikonna/TrekForge fork into plugins, it needs deeper planner extension points.

Requested capabilities:

• Permission-gated write APIs for trips, days, itinerary assignments, and places
• Plugin metadata attached to core entities without schema forks
• Native planner UI slots for sidebars, toolbars, place details, route details, and item actions
• Route provider APIs for transit, multimodal routing, and external route services
• Scheduling hooks for duration, travel time, constraints, and recalculation
• Structured validation/warning contributions
• Place-detail providers for photos, reviews, popular times, ratings, and external metadata

Goal: allow downstream features to be implemented as plugins instead of long-lived core patches, while preserving plugin permissions, isolation, and maintainability.

[SimMesg20]

Id like to second this, i am currently building the old budget planner as a plugin and id like to have it life in the trip aswell. So i would need the ability to at least add a page to the Trip itself not the dashboard

[mauriceboe]

Thanks @hykilpikonna and @SimMesg20.

I'm working on a major expansion of the plugin system in our Fix 3.2.1.