feat: implement CMS for content management (WEB-02/03/04/06)

Introduces Filament management for site settings, services, portfolio cases, and testimonials with admin-only policies, validated media uploads, and deterministic seeding. Includes comprehensive design and task documentation for the implementation.

Co-authored-by: Cursor <cursoragent@cursor.com>

openspec/changes/archive/2026-07-29-build-content-cms/specs/testimonials/spec.md

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+## ADDED Requirements
+
+### Requirement: Testimonials are managed with publication control
+
+The system SHALL allow admins to manage testimonials (SPEC WEB-04) with quote text, author name, optional context, optional photo with alt text, sort order, featured flag, and `published_at`.
+
+#### Scenario: Unpublished testimonial is excluded
+
+- **WHEN** a testimonial has `published_at` null
+- **THEN** the `published()` scope MUST exclude it
+
+#### Scenario: Published testimonial is queryable
+
+- **WHEN** an admin sets `published_at` with required quote and author name
+- **THEN** the testimonial MUST be included in the `published()` scope
+
+#### Scenario: Assistant cannot manage testimonials
+
+- **WHEN** an assistant attempts to access the testimonials Resource
+- **THEN** access MUST be denied with HTTP 403
+
+#### Scenario: Featured testimonials are filterable
+
+- **WHEN** content is queried with featured filter
+- **THEN** records with `is_featured` true MUST be retrievable independently of sort order