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

ui/storybook/stories/dialogs-modals.stories.tsx

@@ -561,7 +561,7 @@ function IssueDialogOpener({
   return <NewIssueDialog />;
 }
 
-function AgentDialogOpener({ advanced }: { advanced?: boolean }) {
+function AgentDialogOpener({ variant = "recommendation" }: { variant?: "recommendation" | "advanced" | "invite" }) {
   const { openNewAgent } = useDialog();
 
   useOpenWhenCompanyReady(() => {
@@ -569,12 +569,12 @@ function AgentDialogOpener({ advanced }: { advanced?: boolean }) {
   });
 
   useEffect(() => {
-    if (!advanced) return undefined;
+    if (variant === "recommendation") return undefined;
     const timer = window.setTimeout(() => {
-      clickButtonByText("advanced configuration");
+      clickButtonByText(variant === "advanced" ? "Configure a runtime" : "Invite an external agent");
     }, 250);
     return () => window.clearTimeout(timer);
-  }, [advanced]);
+  }, [variant]);
 
   return <NewAgentDialog />;
 }
@@ -963,7 +963,21 @@ export const NewAgentAdapterSelection: Story = {
       description="Advanced branch of the agent creation wizard showing registered adapter choices and recommended states."
       badges={["populated", "adapters", "advanced"]}
     >
-      <AgentDialogOpener advanced />
+      <AgentDialogOpener variant="advanced" />
+    </DialogStory>
+  ),
+};
+
+export const NewAgentExternalInvite: Story = {
+  name: "New Agent - External Invite",
+  render: () => (
+    <DialogStory
+      eyebrow="NewAgentDialog"
+      title="External agent invite"
+      description="Agent onboarding prompt generation inside the add-agent modal."
+      badges={["agent invite", "onboarding", "approval"]}
+    >
+      <AgentDialogOpener variant="invite" />
     </DialogStory>
   ),
 };