feat(admin): standalone Projects page + per-project asset manager

- content-svc: GET /v1/projects (browse/search all projects across containers,
  paginated, admin) returning template name/slug + AE status; project_assets
  table (mig 23) + entity; GET/POST/DELETE /v1/projects/{id}/assets
- /admin/projects: searchable, paginated list of every renderable project with
  thumbnail, template, aspect/resolution, AE-file + publish status
- ProjectAssets component: list/upload/delete named footage/image/audio/font
  files per project (reused in the projects page; AE file upload alongside)
- nav + fa/en "Projects" label

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/db/migrations/23_content_project_assets.sql

@@ -0,0 +1,20 @@
+-- =====================================================================
+-- CONTENT SCHEMA — Part 23: per-project assets (footage / images / audio / fonts)
+-- Named asset files attached to a renderable project, alongside its .aep.
+-- =====================================================================
+
+SET search_path TO content, public;
+
+CREATE TABLE IF NOT EXISTS project_assets (
+    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    project_id  UUID        NOT NULL,
+    name        TEXT        NOT NULL,
+    kind        TEXT        NOT NULL DEFAULT 'footage',  -- footage | image | audio | font | other
+    url         TEXT        NOT NULL,
+    minio_key   TEXT,
+    size_bytes  BIGINT,
+    sort        INT         NOT NULL DEFAULT 0,
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_project_assets_project ON project_assets (project_id, sort);