## Description
The membership reconciliation ensures the prebuilds system user is a
member of all organizations with prebuilds configured. To support
prebuilds quota management, each organization must have a prebuilds
group that the system user belongs to.
## Problem
Previously, membership reconciliation iterated over all presets to check
and update membership status. This meant database queries
`GetGroupByOrgAndName` and `InsertGroupMember` were executed for each
preset. Since presets are unique combinations of `(organization,
template, template version, preset)`, this resulted in several redundant
checks for the same organization.
In dogfood, `InsertGroupMember` was called thousands of times per day,
even though memberships were already configured ([internal Grafana
dashboard link](https://grafana.dev.coder.com/goto/46MZ1UgDg?orgId=1))
<img width="5382" height="1788" alt="Screenshot 2025-10-28 at 16 01 36"
src="https://github.com/user-attachments/assets/757b7253-106f-4f72-8586-8e2ede9f18db"
/>
## Solution
This PR introduces `GetOrganizationsWithPrebuildStatus`, a single query
that returns:
* All unique organizations with prebuilds configured
* Whether the prebuilds user is a member of each organization
* Whether the prebuilds group exists in each organization
* Whether the prebuilds user is in the prebuilds group
The membership reconciliation logic now:
* Fetches status for all organizations in one query
* Only performs inserts for organizations missing required memberships
or groups
* Safely handles concurrent operations via unique constraint violations
* This reduces database load from `O(presets)` to `O(organizations)` per
reconciliation loop, with a single read query when everything is
configured.
## Changes
* Add `GetOrganizationsWithPrebuildStatus` SQL query
* Update `membership.ReconcileAll` to use organization-based
reconciliation instead of preset-based
* Update tests to reflect new behavior
Related to internal thread:
https://codercom.slack.com/archives/C07GRNNRW03/p1760535570381369
Susana Ferreira
7e8fcb4b0f