feat: content V2 docs — malleable-first architecture, templates optional (#100)

* feat: content V2 docs — malleable-first architecture, templates optional

- OpenAPI: move PATCH edit from /video to /content, add image_url input
- OpenAPI: ContentTemplate schema — rename name→id, drop defaultLipsync
- OpenAPI: add GET /api/content/templates/{id} detail endpoint
- OpenAPI: add template field to video, image, text primitive schemas
- OpenAPI: make pipeline template optional (remove default)
- OpenAPI: remove V1 artifacts (era_config, pipeline_config)
- Guide: new content.mdx — primitives, templates, override priority, video modes
- Guide: update content-agent.mdx — template is optional
- Nav: add Content group to Guides tab

Made-with: Cursor

* docs: link template params to List Templates endpoint

Add cross-reference links to GET /api/content/templates in all template
parameter descriptions so devs and AI can easily discover available options.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: merge content.mdx into content-agent, rename to Content

Consolidated the orphaned content.mdx (primitives, templates, video modes,
iteration guide) into content-agent.mdx and renamed the page title to
"Content". Deleted content.mdx since it wasn't in the navigation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: address CodeRabbit review feedback on OpenAPI spec

1. ContentCreateResponse: remove template from required, allow null
2. ContentTemplateDetail: add full operation properties to edit schema
3. Remove duplicate PATCH /api/content/video (keep PATCH /api/content)
4. Add missing Music schemas (MusicComposeRequest, MusicComposeDetailedRequest,
   MusicStreamRequest, MusicCreatePlanRequest, MusicCreatePlanResponse,
   MusicErrorResponse)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Sweets Sweetman <sweetmantech@gmail.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

api-reference/content/edit.mdx

@@ -1,4 +1,4 @@
 ---
 title: 'Edit Content'
-openapi: 'PATCH /api/content/video'
+openapi: 'PATCH /api/content'
 ---

api-reference/content/template-detail.mdx

@@ -0,0 +1,4 @@
+---
+title: 'Get Template Detail'
+openapi: 'GET /api/content/templates/{id}'
+---