Epic: Full embeddable EmailTemplateAdmin page component

[patoperpetua]

Objective

Ship a complete embeddable EmailTemplateAdmin React page in @singleton-sd/post-kit-editor so consumers mount one component and only wire list/save/send-test callbacks. The canvas must match the official EmailBuilder.js playground UX (MUI inspector + samples), not the current skinny hand-rolled canvas.

Locked decisions

• Hosting: embeddable package component only (not a PostKit-hosted apps/ CMS).
• Canvas: port usewaypoint/email-builder-js examples/vite-emailbuilder-mui (inspector, samples drawer, template panel).
• Boundary unchanged: no API keys in the browser; no disk/Git/Azure I/O inside the package; save/send remain consumer callbacks.

Target consumer API

import { EmailTemplateAdmin } from '@singleton-sd/post-kit-editor';

<EmailTemplateAdmin
  templates={catalog}
  onSave={saveToConsumerApi}
  onSendTest={postSendTestToBff}
/>

Work

• Vendor/adapt EmailBuilder MUI sample into post-kit-editor; swap default canvas
• EmailTemplateAdmin page (list + PostKit chrome + new canvas); export + ThemeProvider
• Slim examples/admin-editor + editor-integration docs to one-component embedding

Out of scope

• Hosted multi-tenant CMS under apps/
• Real GitHub App / consumer SSO inside the package
• Changing compile/publish/Blob contracts (template.json remains EmailBuilder JSON)

Acceptance criteria

• A consumer can mount EmailTemplateAdmin and get list + EmailBuilder playground-quality canvas + PostKit metadata/preview/save/send without rebuilding admin chrome.
• Existing EmailTemplateEditor / EmailBuilderCanvas remain exported for advanced hosts.
• Docs and examples/admin-editor default to the one-component model.

[patoperpetua]

Decomposed into child issues

Issue	Scope
#139	Port EmailBuilder MUI sample canvas
#140	EmailTemplateAdmin page component
#	Slim example + docs

Sequencing: #139 first (claimable now). #140 depends on #139. # depends on #140.

[patoperpetua]

Implementation PR opened for all children: see the linked PR that closes #139, #140, and #141.

After merge, this epic can be closed if acceptance criteria are satisfied.