feat(addons): GitHub settings page, registration and docs

Add the GitHub connection page (fine-grained token, repository list,
read-only note, Test that checks each listed repository), let the shared
connector page hide messaging settings for a kind that carries no
messages, register the add-on in the package matrix and the catalog, and
document the credential slot and the GitHub add-on.

Assisted-by: Claude:claude-sonnet-5-5 [go node]

addons/github/ui/src/addon.jsx

@@ -0,0 +1,92 @@
+/* eslint-disable no-unused-vars -- components used only inside JSX look unused to this config, which has no eslint-plugin-react */
+import { RouteProvider } from 'react-router-dom'
+import { getSdk, } from '../../../internal/host-compat/src/runtime.js'
+import { registerLocales } from '../../../internal/host-compat/src/i18n.js'
+import ConnectorPage from '../../../internal/connector-ui/src/ConnectorPage'
+import { Field, FieldError, Notice, TextInput } from '../../../internal/connector-ui/src/controls'
+import en from './i18n/github.en.json'
+import { checkLine, extraBody, extraForm, extraValid, githubSecret, parseRepos, reposProblem, tokenProblem } from './repos'
+
+registerLocales({ github: { en } })
+
+// The fine-grained token. It is typed only to replace it.
+function GitHubToken({ form, setForm, t }) {
+  const problem = tokenProblem(form)
+  return (
+    <Field label={t('token')} hint={t('tokenHelp')}>
+      {(p) => (
+        <TextInput {...p} mono type="password" autoComplete="off" value={form.token || ''} required={!form.id}
+          placeholder={form.id ? t('tokenSaved') : ''} aria-invalid={problem ? 'true' : undefined}
+          onChange={(e) => setForm({ ...form, token: e.target.value })} />
+      )}
+    </Field>
+  )
+}
+
+// The repositories the agent may read. The host refuses any other one before
+// the add-on is called.
+function GitHubFields({ form, setForm, t }) {
+  const problem = reposProblem(form.repos_text)
+  const count = parseRepos(form.repos_text).length
+  return (
+    <>
+      {tokenProblem(form) && <FieldError role="status" data-testid="token-problem">{t(tokenProblem(form))}</FieldError>}
+      <Field label={t('repos')} hint={t('reposHelp', { count })}>
+        {(p) => (
+          <textarea {...p} className="cn-input cn-input--mono" rows={5} data-testid="github-repos" value={form.repos_text || ''}
+            placeholder="owner/name" aria-invalid={problem ? 'true' : undefined}
+            onChange={(e) => setForm({ ...form, repos_text: e.target.value })} />
+        )}
+      </Field>
+      {problem && <FieldError role="status" data-testid="repos-problem">{t(problem)}</FieldError>}
+      <Notice tone="info" role="note" testId="github-write-mode">{t('writeOff')}</Notice>
+    </>
+  )
+}
+
+function Help({ t }) {
+  return (
+    <details className="cn-help" data-testid="github-setup">
+      <summary>{t('setup.title')}</summary>
+      <ol>
+        <li>{t('setup.step1')}</li>
+        <li>{t('setup.step2')}</li>
+        <li>{t('setup.step3')}</li>
+      </ol>
+    </details>
+  )
+}
+
+function RowInfo({ c, t }) {
+  const repos = c.resources || []
+  return <span className="cn-muted" data-testid="github-row-repos">{repos.length === 0 ? t('noRepos') : t('reposOf', { count: repos.length, list: repos.join(', ') })}</span>
+}
+
+// The Test button: the host asks who the token is; this asks, for each listed
+// repository, whether the token reaches it.
+async function testExtra(c, t) {
+  const lines = []
+  for (const repo of c.resources || []) {
+    try {
+      const r = await getSdk().api.read({ arguments: { tool: 'check', repo } })
+      lines.push(checkLine(r?.data ? { ...r.data, repo } : { repo, reachable: false }, t))
+    } catch (_e) {
+      lines.push(checkLine({ repo, reachable: false }, t))
+    }
+  }
+  return lines.join(' ')
+}
+
+export function createGitHub() {
+  function Component({ page, path, search }) {
+    if (page !== 'apps') return null
+    return (
+      <RouteProvider value={{ page, path: path || '', search: search || '' }}>
+        <ConnectorPage kind="github" ns="github" testId="github-page" TokenFields={GitHubToken} tokenOf={githubSecret} messaging={false}
+          ExtraFields={GitHubFields} extraBody={extraBody} extraForm={extraForm} extraValid={extraValid} testExtra={testExtra}
+          Help={Help} RowInfo={RowInfo} />
+      </RouteProvider>
+    )
+  }
+  return { Component, components: {}, chatActions: [], dispose() {} }
+}