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>

packages/plugins/examples/plugin-file-browser-example/src/worker.ts

@@ -106,43 +106,46 @@ const plugin = definePlugin({
       }));
     });
 
-    ctx.data.register(
-      "fileList",
-      async (params: Record<string, unknown>) => {
-        const projectId = params.projectId as string;
-        const companyId = typeof params.companyId === "string" ? params.companyId : "";
-        const workspaceId = params.workspaceId as string;
-        const directoryPath = typeof params.directoryPath === "string" ? params.directoryPath : "";
-        if (!projectId || !companyId || !workspaceId) return { entries: [] };
-        const workspaces = await ctx.projects.listWorkspaces(projectId, companyId);
-        const workspace = workspaces.find((w) => w.id === workspaceId);
-        if (!workspace) return { entries: [] };
-        const workspacePath = sanitizeWorkspacePath(workspace.path);
-        if (!workspacePath) return { entries: [] };
-        const dirPath = resolveWorkspace(workspacePath, directoryPath);
-        if (!dirPath) {
-          return { entries: [] };
-        }
-        if (!fs.existsSync(dirPath) || !fs.statSync(dirPath).isDirectory()) {
-          return { entries: [] };
-        }
-        const names = fs.readdirSync(dirPath).sort((a, b) => a.localeCompare(b));
-        const entries = names.map((name) => {
-          const full = path.join(dirPath, name);
-          const stat = fs.lstatSync(full);
-          const relativePath = path.relative(workspacePath, full);
-          return {
-            name,
-            path: relativePath,
-            isDirectory: stat.isDirectory(),
-          };
-        }).sort((a, b) => {
-          if (a.isDirectory !== b.isDirectory) return a.isDirectory ? -1 : 1;
-          return a.name.localeCompare(b.name);
-        });
-        return { entries };
-      },
-    );
+    async function readFileList(params: Record<string, unknown>) {
+      const projectId = params.projectId as string;
+      const companyId = typeof params.companyId === "string" ? params.companyId : "";
+      const workspaceId = params.workspaceId as string;
+      const directoryPath = typeof params.directoryPath === "string" ? params.directoryPath : "";
+      if (!projectId || !companyId || !workspaceId) return { entries: [] };
+      const workspaces = await ctx.projects.listWorkspaces(projectId, companyId);
+      const workspace = workspaces.find((w) => w.id === workspaceId);
+      if (!workspace) return { entries: [] };
+      const workspacePath = sanitizeWorkspacePath(workspace.path);
+      if (!workspacePath) return { entries: [] };
+      const dirPath = resolveWorkspace(workspacePath, directoryPath);
+      if (!dirPath) {
+        return { entries: [] };
+      }
+      if (!fs.existsSync(dirPath) || !fs.statSync(dirPath).isDirectory()) {
+        return { entries: [] };
+      }
+      const names = fs.readdirSync(dirPath).sort((a, b) => a.localeCompare(b));
+      const entries = names.map((name) => {
+        const full = path.join(dirPath, name);
+        const stat = fs.lstatSync(full);
+        const relativePath = path.relative(workspacePath, full);
+        return {
+          name,
+          path: relativePath,
+          isDirectory: stat.isDirectory(),
+        };
+      }).sort((a, b) => {
+        if (a.isDirectory !== b.isDirectory) return a.isDirectory ? -1 : 1;
+        return a.name.localeCompare(b.name);
+      });
+      return { entries };
+    }
+
+    ctx.data.register("fileList", readFileList);
+
+    // Mirror `fileList` as an action so the UI can lazily fetch directory
+    // children on tree expand without spawning a usePluginData hook per dir.
+    ctx.actions.register("loadFileList", readFileList);
 
     ctx.data.register(
       "fileContent",