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/db/src/migrations/0076_useful_elektra.sql

@@ -0,0 +1,29 @@
+CREATE TABLE IF NOT EXISTS "plugin_managed_resources" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"company_id" uuid NOT NULL,
+	"plugin_id" uuid NOT NULL,
+	"plugin_key" text NOT NULL,
+	"resource_kind" text NOT NULL,
+	"resource_key" text NOT NULL,
+	"resource_id" uuid NOT NULL,
+	"defaults_json" jsonb DEFAULT '{}'::jsonb NOT NULL,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL,
+	"updated_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+DO $$ BEGIN
+	ALTER TABLE "plugin_managed_resources" ADD CONSTRAINT "plugin_managed_resources_company_id_companies_id_fk" FOREIGN KEY ("company_id") REFERENCES "public"."companies"("id") ON DELETE cascade ON UPDATE no action;
+EXCEPTION
+	WHEN duplicate_object THEN NULL;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+	ALTER TABLE "plugin_managed_resources" ADD CONSTRAINT "plugin_managed_resources_plugin_id_plugins_id_fk" FOREIGN KEY ("plugin_id") REFERENCES "public"."plugins"("id") ON DELETE cascade ON UPDATE no action;
+EXCEPTION
+	WHEN duplicate_object THEN NULL;
+END $$;
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "plugin_managed_resources_company_idx" ON "plugin_managed_resources" USING btree ("company_id");--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "plugin_managed_resources_plugin_idx" ON "plugin_managed_resources" USING btree ("plugin_id");--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "plugin_managed_resources_resource_idx" ON "plugin_managed_resources" USING btree ("resource_kind","resource_id");--> statement-breakpoint
+CREATE UNIQUE INDEX IF NOT EXISTS "plugin_managed_resources_company_plugin_resource_uq" ON "plugin_managed_resources" USING btree ("company_id","plugin_id","resource_kind","resource_key");

packages/db/src/migrations/meta/_journal.json

@@ -533,6 +533,13 @@
       "when": 1777572332006,
       "tag": "0075_cultured_sebastian_shaw",
       "breakpoints": true
+    },
+    {
+      "idx": 76,
+      "version": "7",
+      "when": 1777675301279,
+      "tag": "0076_useful_elektra",
+      "breakpoints": true
     }
   ]
-}
+}