Improve external agent invite flow (#6183)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies.
> - Agent creation can happen through local runtimes, managed runtimes,
and external agents that onboard through invites.
> - The old OpenClaw-oriented invite UX lived under company
settings/invites and made a gateway-specific path look like a company
access setting.
> - That hid the broader bring-your-own-agent flow and forced operators
to leave the add-agent modal when adding an external agent.
> - This pull request moves external agent invite generation into the
add-agent modal and makes the copy agent-oriented instead of
OpenClaw-only.
> - The benefit is a clearer agent-first onboarding path while company
invites stay focused on human access.

## What Changed

- Added an external-agent invite branch to the add-agent modal,
including a dedicated prompt result view with Back navigation.
- Added a shared agent onboarding prompt builder and focused modal
coverage for prompt replacement/back navigation.
- Removed the agent invite prompt UI from Company Settings and Company
Invites, leaving Company Invites focused on human access links and
invite history.
- Updated the hidden OpenClaw Gateway runtime hint to direct operators
to the add-agent invite flow instead of presenting it as a blocked
runtime card.
- Updated invite/onboarding docs, storybook coverage, and server-side
onboarding copy toward generic agent language while preserving existing
gateway compatibility.

## Verification

- `pnpm -r typecheck`
- `pnpm build`
- `FAKE_BIN="$(mktemp -d)/bin"; mkdir -p "$FAKE_BIN"; printf
'#!/bin/sh\nexit 1\n' > "$FAKE_BIN/tailscale"; chmod +x
"$FAKE_BIN/tailscale"; PATH="$FAKE_BIN:$PATH" pnpm test:run`
- `pnpm test:run` without the fake `tailscale` shim was also attempted;
it failed only in two pre-existing CLI tailnet fallback tests because
this host has a real Tailscale address (`100.125.202.3`) where those
tests expect no Tailscale.
- Focused confirmation for that host-env issue: `FAKE_BIN=...
PATH="$FAKE_BIN:$PATH" pnpm exec vitest run --project paperclipai
cli/src/__tests__/network-bind.test.ts
cli/src/__tests__/onboard.test.ts`
- Manual UI verification: served UI locally in light mode, opened
add-agent modal, generated external agent prompt, verified the generated
prompt replaces the form and Back returns to the form.

### Screenshots

![Add agent
modal](https://raw.githubusercontent.com/aronprins/paperclip/pr-assets/6183-agent-invites/.github/pr-screenshots/6183/add-agent-modal-light.png)

![External agent invite
form](https://raw.githubusercontent.com/aronprins/paperclip/pr-assets/6183-agent-invites/.github/pr-screenshots/6183/external-agent-invite-form-light.png)

![Generated onboarding prompt replacement
view](https://raw.githubusercontent.com/aronprins/paperclip/pr-assets/6183-agent-invites/.github/pr-screenshots/6183/onboarding-prompt-result-light.png)

## Risks

- Existing OpenClaw gateway compatibility remains, but operators now
discover external agent onboarding from the add-agent modal instead of
company settings.
- Agent invites still appear in the invite history table, so that page
may show agent-scoped invite rows even though it no longer creates agent
onboarding prompts.
- Low migration risk: no schema changes.

> 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 in Codex desktop; tool-enabled
repository, shell, browser, and 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

server/src/__tests__/heartbeat-comment-wake-batching.test.ts

@@ -766,13 +766,19 @@ describe("heartbeat comment wake batching", () => {
 
       gateway.releaseFirstWait();
 
-      await waitFor(() => gateway.getAgentPayloads().length === 2, 90_000);
+      await waitFor(() => gateway.getAgentPayloads().length >= 2, 90_000);
       await waitFor(async () => {
         const runs = await db
           .select()
           .from(heartbeatRuns)
-          .where(eq(heartbeatRuns.agentId, agentId));
-        return runs.length === 2 && runs.every((run) => run.status === "succeeded");
+          .where(eq(heartbeatRuns.agentId, agentId))
+          .orderBy(asc(heartbeatRuns.createdAt));
+        const [initialRun, promotedRun] = runs;
+        return (
+          initialRun?.id === firstRun?.id &&
+          initialRun.status === "succeeded" &&
+          promotedRun?.status === "succeeded"
+        );
       }, 90_000);
 
       const reopenedIssue = await db