Clarify sandbox provider messaging in company environments (#4902)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies.
> - Company Environments is the operator-facing seam for choosing where
compatible adapters execute work.
> - Sandbox provider plugins such as E2B extend that seam, but they are
not agent adapters themselves.
> - The current Company Environments copy put adapter capability rows
and sandbox-provider enablement on the same page without clearly
distinguishing the two concepts.
> - That made it look like installing the E2B sandbox provider caused a
new adapter to appear under adapters.
> - This pull request clarifies the UI language so provider plugins are
described as backing the Sandbox driver rather than being adapter types.
> - The benefit is a more accurate mental model for operators
configuring environments and adapters.

## What Changed

- Added explicit Company Environments copy stating that installed
sandbox providers are not adapter types and instead back the Sandbox
driver for compatible adapters.
- Renamed the support-matrix column from `Sandbox` to `Sandbox via
plugin` to make the provider relationship visible in the table itself.
- Extended the existing environments UI test to assert the new
clarification text.

## Verification

- `pnpm test -- --run ui/src/pages/CompanySettings.test.tsx`
Result: could not complete cleanly in this worktree because the checkout
is missing its local workspace install links.
- Direct Vitest fallback against `ui/src/pages/CompanySettings.test.tsx`
Result: failed before test collection on local dependency resolution
(`react/jsx-dev-runtime`), so there is no passing automated signal from
this checkout.
- Manual review
Confirm the Company Environments page now says sandbox providers are not
adapter types and labels the table column as `Sandbox via plugin`.

## Risks

- Low risk. This is a copy-only UI clarification plus a matching test
assertion; the main risk is wording drift if the product later decides
sandbox providers should be surfaced differently.

## Model Used

- OpenAI Codex via the local `codex_local` Paperclip adapter. This run
used tool-assisted code editing and shell execution. The exact backend
model ID and context window are not exposed in the Paperclip run context
for this session.

## 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
- [ ] 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
- [ ] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [ ] I will address all Greptile and reviewer comments before
requesting merge

ui/src/pages/CompanySettings.test.tsx

@@ -220,6 +220,10 @@ describe("CompanyEnvironments", () => {
     await flushReact();
     await flushReact();
 
+    expect(container.textContent).toContain("Installed sandbox providers:");
+    expect(container.textContent).toContain("Secure Sandbox");
+    expect(container.textContent).toContain("These are not adapter types.");
+
     const editButton = Array.from(container.querySelectorAll("button"))
       .find((button) => button.textContent?.trim() === "Edit");
     expect(editButton).toBeTruthy();