Add SSH environment support (#4358)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - The environments subsystem already models execution environments,
but before this branch there was no end-to-end SSH-backed runtime path
for agents to actually run work against a remote box
> - That meant agents could be configured around environment concepts
without a reliable way to execute adapter sessions remotely, sync
workspace state, and preserve run context across supported adapters
> - We also need environment selection to participate in normal
Paperclip control-plane behavior: agent defaults, project/issue
selection, route validation, and environment probing
> - Because this capability is still experimental, the UI surface should
be easy to hide and easy to remove later without undoing the underlying
implementation
> - This pull request adds SSH environment execution support across the
runtime, adapters, routes, schema, and tests, then puts the visible
environment-management UI behind an experimental flag
> - The benefit is that we can validate real SSH-backed agent execution
now while keeping the user-facing controls safely gated until the
feature is ready to come out of experimentation

## What Changed

- Added SSH-backed execution target support in the shared adapter
runtime, including remote workspace preparation, skill/runtime asset
sync, remote session handling, and workspace restore behavior after
runs.
- Added SSH execution coverage for supported local adapters, plus remote
execution tests across Claude, Codex, Cursor, Gemini, OpenCode, and Pi.
- Added environment selection and environment-management backend support
needed for SSH execution, including route/service work, validation,
probing, and agent default environment persistence.
- Added CLI support for SSH environment lab verification and updated
related docs/tests.
- Added the `enableEnvironments` experimental flag and gated the
environment UI behind it on company settings, agent configuration, and
project configuration surfaces.

## Verification

- `pnpm exec vitest run
packages/adapters/claude-local/src/server/execute.remote.test.ts
packages/adapters/cursor-local/src/server/execute.remote.test.ts
packages/adapters/gemini-local/src/server/execute.remote.test.ts
packages/adapters/opencode-local/src/server/execute.remote.test.ts
packages/adapters/pi-local/src/server/execute.remote.test.ts`
- `pnpm exec vitest run server/src/__tests__/environment-routes.test.ts`
- `pnpm exec vitest run
server/src/__tests__/instance-settings-routes.test.ts`
- `pnpm exec vitest run ui/src/lib/new-agent-hire-payload.test.ts
ui/src/lib/new-agent-runtime-config.test.ts`
- `pnpm -r typecheck`
- `pnpm build`
- Manual verification on a branch-local dev server:
  - enabled the experimental flag
  - created an SSH environment
  - created a Linux Claude agent using that environment
- confirmed a run executed on the Linux box and synced workspace changes
back

## Risks

- Medium: this touches runtime execution flow across multiple adapters,
so regressions would likely show up in remote session setup, workspace
sync, or environment selection precedence.
- The UI flag reduces exposure, but the underlying runtime and route
changes are still substantial and rely on migration correctness.
- The change set is broad across adapters, control-plane services,
migrations, and UI gating, so review should pay close attention to
environment-selection precedence and remote workspace lifecycle
behavior.

## Model Used

- OpenAI Codex via Paperclip's local Codex adapter, GPT-5-class coding
model with tool use and code execution in the local repo workspace. The
local adapter does not surface a more specific public model version
string in this branch workflow.

## 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
- [ ] 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

server/src/__tests__/instance-settings-routes.test.ts

@@ -55,6 +55,7 @@ describe("instance settings routes", () => {
       feedbackDataSharingPreference: "prompt",
     });
     mockInstanceSettingsService.getExperimental.mockResolvedValue({
+      enableEnvironments: false,
       enableIsolatedWorkspaces: false,
       autoRestartDevServerWhenIdle: false,
     });
@@ -69,6 +70,7 @@ describe("instance settings routes", () => {
     mockInstanceSettingsService.updateExperimental.mockResolvedValue({
       id: "instance-settings-1",
       experimental: {
+        enableEnvironments: true,
         enableIsolatedWorkspaces: true,
         autoRestartDevServerWhenIdle: false,
       },
@@ -87,6 +89,7 @@ describe("instance settings routes", () => {
     const getRes = await request(app).get("/api/instance/settings/experimental");
     expect(getRes.status).toBe(200);
     expect(getRes.body).toEqual({
+      enableEnvironments: false,
       enableIsolatedWorkspaces: false,
       autoRestartDevServerWhenIdle: false,
     });
@@ -120,6 +123,24 @@ describe("instance settings routes", () => {
     });
   });
 
+  it("allows local board users to update environment controls", async () => {
+    const app = await createApp({
+      type: "board",
+      userId: "local-board",
+      source: "local_implicit",
+      isInstanceAdmin: true,
+    });
+
+    await request(app)
+      .patch("/api/instance/settings/experimental")
+      .send({ enableEnvironments: true })
+      .expect(200);
+
+    expect(mockInstanceSettingsService.updateExperimental).toHaveBeenCalledWith({
+      enableEnvironments: true,
+    });
+  });
+
   it("allows local board users to read and update general settings", async () => {
     const app = await createApp({
       type: "board",