feat: CMS de conteúdo do site (WEB-02/03/04/06)

Implementa gestão Filament de configurações, serviços, portfólio e depoimentos com policies admin-only, upload validado e seed determinístico.

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

openspec/changes/build-content-cms/specs/portfolio-cases/spec.md

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+## ADDED Requirements
+
+### Requirement: Portfolio cases support editorial content and ordered gallery
+
+The system SHALL allow admins to manage portfolio cases (SPEC WEB-03) with title, unique slug, summary, event type, optional city/venue/event date, challenge, solution, optional result, cover image with alt text, featured flag, sort order, `published_at`, and optional SEO meta fields. Each case MUST support an ordered gallery via `portfolio_images` (path, alt text, optional caption, sort order).
+
+#### Scenario: Draft case is not publicly visible
+
+- **WHEN** a portfolio case has `published_at` null
+- **THEN** the `published()` scope MUST exclude it
+
+#### Scenario: Published case meets acceptance criteria
+
+- **WHEN** an admin fills required fields and sets `published_at`
+- **THEN** the case MUST be included in the `published()` scope
+- **AND** cover and gallery images MUST have alt text when present
+
+#### Scenario: Gallery images maintain order
+
+- **WHEN** an admin reorders gallery images in Filament
+- **THEN** `sort_order` MUST reflect the chosen order per `portfolio_case_id`
+
+#### Scenario: Assistant cannot manage portfolio
+
+- **WHEN** an assistant attempts to access portfolio cases
+- **THEN** access MUST be denied with HTTP 403
+
+#### Scenario: Cascade delete removes gallery images
+
+- **WHEN** a portfolio case is deleted
+- **THEN** associated `portfolio_images` records MUST be removed (FK cascade)