[codex] Add resource membership controls (#6677)

## Thinking Path

> - Paperclip orchestrates AI-agent companies through company-scoped
issues, projects, agents, and board-visible workflows.
> - The board sidebar and project list are the daily navigation surface
for that control plane.
> - Users need to keep all projects and agents accessible while hiding
resources they have intentionally left from their own sidebar.
> - That requires user-scoped resource membership state backed by
company-scoped API and database contracts.
> - The branch also needed to preserve HTTP worktree login sessions and
keep the project list easier to scan after membership grouping.
> - This pull request adds resource membership controls, sidebar leave
actions, grouped/sortable project listings, and focused tests.
> - The benefit is a cleaner personal workspace view without weakening
company-scoped access to the underlying project or agent detail pages.

## What Changed

- Added `project_memberships` and `agent_memberships` tables with
API/shared/server contracts for current-user join/leave state.
- Renumbered the membership migration to `0090_resource_memberships`
after rebasing onto current `master`, and made it idempotent for anyone
who had applied the old branch-local `0087` migration.
- Added project and agent sidebar leave actions, plus list filtering
that waits for membership state before hiding resources.
- Added grouped project listing, project sorting controls, and reserved
row subtitle height for cleaner scanning.
- Fixed HTTP auth cookie security handling so HTTP worktree sessions can
persist.
- Updated focused server and UI tests for the new membership, sidebar,
project list, and auth behavior.

## Verification

- `pnpm exec vitest run server/src/__tests__/better-auth.test.ts
server/src/__tests__/resource-memberships-routes.test.ts
ui/src/pages/Projects.test.tsx
ui/src/components/SidebarProjects.test.tsx
ui/src/components/SidebarAgents.test.tsx
ui/src/components/MembershipAction.test.tsx
ui/src/components/EntityRow.test.tsx`
- Confirmed the branch is rebased on current `origin/master`.
- Confirmed the PR diff does not include `pnpm-lock.yaml` or
`.github/workflows` changes.

## Risks

- Migration safety: low to medium. The migration now uses `IF NOT
EXISTS` / guarded constraints and is numbered after current master
migrations, but it should still get CI coverage against fresh databases.
- UI behavior: low. Left resources are hidden from sidebar only after
membership state loads; direct detail access remains available.
- Auth behavior: low. Cookie security is relaxed only for HTTP/private
local-style origins where secure cookies would prevent login
persistence.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI GPT-5 Codex coding agent, tool-enabled shell/git workflow,
context window not exposed by runtime.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

Screenshot note: no browser screenshots were captured in this heartbeat;
the UI changes are covered by focused component tests above.

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/pages/DesignGuide.tsx

@@ -124,6 +124,7 @@ import { InlineEditor } from "@/components/InlineEditor";
 import { PageSkeleton } from "@/components/PageSkeleton";
 import { Identity } from "@/components/Identity";
 import { IssueReferencePill } from "@/components/IssueReferencePill";
+import { MembershipAction } from "@/components/MembershipAction";
 
 /* ------------------------------------------------------------------ */
 /*  Section wrapper                                                    */
@@ -896,6 +897,66 @@ export function DesignGuide() {
             selected
           />
         </div>
+        <SubSection title="Membership action">
+          <div className="border border-border rounded-md">
+            <EntityRow
+              title="Joined resource"
+              subtitle="Hover or focus the row to reveal the reserved action slot."
+              className="group"
+              trailing={
+                <MembershipAction
+                  state="joined"
+                  resourceName="Joined resource"
+                  onJoin={() => {}}
+                  onLeave={() => {}}
+                />
+              }
+            />
+            <EntityRow
+              title="Left resource"
+              subtitle="Persistent action with dimmed row content."
+              className="group text-foreground/55"
+              trailing={
+                <MembershipAction
+                  state="left"
+                  resourceName="Left resource"
+                  onJoin={() => {}}
+                  onLeave={() => {}}
+                />
+              }
+            />
+            <EntityRow
+              title="Leaving resource"
+              subtitle="Disabled while the optimistic mutation is pending."
+              className="group text-foreground/55"
+              trailing={
+                <MembershipAction
+                  state="left"
+                  pending
+                  pendingState="left"
+                  resourceName="Leaving resource"
+                  onJoin={() => {}}
+                  onLeave={() => {}}
+                />
+              }
+            />
+            <EntityRow
+              title="Joining resource"
+              subtitle="The target state is visible immediately while the server confirms."
+              className="group"
+              trailing={
+                <MembershipAction
+                  state="joined"
+                  pending
+                  pendingState="joined"
+                  resourceName="Joining resource"
+                  onJoin={() => {}}
+                  onLeave={() => {}}
+                />
+              }
+            />
+          </div>
+        </SubSection>
       </Section>
 
       {/* ============================================================ */}