Expand plugin host surface (#5205)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - The plugin system is the extension boundary for optional product
capabilities
> - Rich plugins need more than a worker entrypoint: they need scoped
database storage, local project folders, managed agents/routines, host
navigation, and reusable UI components
> - The LLM Wiki work exposed those missing host surfaces while keeping
plugin code outside the core control plane
> - This pull request expands the core plugin host, SDK, server APIs,
and UI bridge so plugins can declare and use those surfaces
> - The benefit is that future plugins can integrate with Paperclip
through documented, validated contracts instead of bespoke server or UI
imports

## What Changed

- Added plugin-managed database namespaces and migration tracking,
including Drizzle schema/migration files and SQL validation for
namespace isolation.
- Added server support for plugin local folders, managed agents, managed
routines, scoped plugin APIs, and plugin operation visibility.
- Expanded shared plugin manifest/types/validators and SDK
host/testing/UI exports for richer plugin surfaces.
- Added reusable UI pieces for file trees, managed routines, resizable
sidebars, route sidebars, and plugin bridge initialization.
- Updated plugin docs and example plugins to use the expanded host and
SDK surface.

## Verification

- `pnpm install --frozen-lockfile`
- `pnpm run preflight:workspace-links && pnpm exec vitest run
packages/shared/src/validators/plugin.test.ts
server/src/__tests__/plugin-database.test.ts
server/src/__tests__/plugin-local-folders.test.ts
server/src/__tests__/plugin-managed-agents.test.ts
server/src/__tests__/plugin-managed-routines.test.ts
server/src/__tests__/plugin-orchestration-apis.test.ts
ui/src/api/plugins.test.ts ui/src/components/FileTree.test.tsx
ui/src/components/ResizableSidebarPane.test.tsx
ui/src/pages/PluginPage.test.tsx ui/src/plugins/bridge.test.ts` passed:
11 files, 67 tests.
- Confirmed this PR changes 89 files and does not include
`pnpm-lock.yaml` or `.github/workflows/*`.

## Risks

- Medium: this expands plugin host contracts across db/shared/server/ui
and includes a new core migration (`0076_useful_elektra.sql`).
- The plugin database namespace validator is intentionally restrictive;
plugin authors may need follow-up affordances for SQL patterns that
remain blocked.
- Merge this before the LLM Wiki plugin PR so the plugin can resolve the
new SDK and host APIs.

> 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 Codex, GPT-5 coding agent, tool-enabled shell/git/GitHub
workflow. Context window size was not exposed by the 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

---------

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

server/src/services/plugin-capability-validator.ts

@@ -47,6 +47,12 @@ const OPERATION_CAPABILITIES: Record<string, readonly PluginCapability[]> = {
   "companies.get": ["companies.read"],
   "projects.list": ["projects.read"],
   "projects.get": ["projects.read"],
+  "projects.managed.get": ["projects.managed"],
+  "projects.managed.reconcile": ["projects.managed"],
+  "projects.managed.reset": ["projects.managed"],
+  "routines.managed.get": ["routines.managed"],
+  "routines.managed.reconcile": ["routines.managed"],
+  "routines.managed.reset": ["routines.managed"],
   "project.workspaces.list": ["project.workspaces.read"],
   "project.workspaces.get": ["project.workspaces.read"],
   "issues.list": ["issues.read"],
@@ -56,6 +62,9 @@ const OPERATION_CAPABILITIES: Record<string, readonly PluginCapability[]> = {
   "issue.comments.get": ["issue.comments.read"],
   "agents.list": ["agents.read"],
   "agents.get": ["agents.read"],
+  "agents.managed.get": ["agents.managed"],
+  "agents.managed.reconcile": ["agents.managed"],
+  "agents.managed.reset": ["agents.managed"],
   "goals.list": ["goals.read"],
   "goals.get": ["goals.read"],
   "activity.list": ["activity.read"],
@@ -65,6 +74,12 @@ const OPERATION_CAPABILITIES: Record<string, readonly PluginCapability[]> = {
   "issues.summaries.getOrchestration": ["issues.orchestration.read"],
   "db.namespace": ["database.namespace.read"],
   "db.query": ["database.namespace.read"],
+  "localFolders.declarations": [],
+  "localFolders.configure": ["local.folders"],
+  "localFolders.status": ["local.folders"],
+  "localFolders.list": ["local.folders"],
+  "localFolders.readText": ["local.folders"],
+  "localFolders.writeTextAtomic": ["local.folders"],
 
   // Data write operations
   "issues.create": ["issues.create"],
@@ -133,6 +148,7 @@ const UI_SLOT_CAPABILITIES: Record<PluginUiSlotType, PluginCapability> = {
   commentAnnotation: "ui.commentAnnotation.register",
   commentContextMenuItem: "ui.action.register",
   settingsPage: "instance.settings.register",
+  routeSidebar: "ui.sidebar.register",
 };
 
 /**
@@ -167,6 +183,9 @@ const FEATURE_CAPABILITIES: Record<string, PluginCapability> = {
   webhooks: "webhooks.receive",
   database: "database.namespace.migrate",
   environmentDrivers: "environment.drivers.register",
+  agents: "agents.managed",
+  projects: "projects.managed",
+  routines: "routines.managed",
 };
 
 // ---------------------------------------------------------------------------