Feat: Gate API docs endpoints behind API_DOCS_ENABLED env var

When API_DOCS_ENABLED=false, FastAPI registers no routes for /docs,
/redoc, or /openapi.json, returning 404 for all three. Default is true
for backwards compatibility. Invalid values fall back to true (FR-007).

Fix: Remove tests/ and alembic/ from api/.dockerignore so the test
Dockerfile (which uses COPY . .) includes the test suite; Dockerfile.prod
is unaffected as it only copies app/ explicitly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

specs/012-api-docs-gate/checklists/requirements.md

@@ -0,0 +1,34 @@
+# Specification Quality Checklist: API Documentation Visibility Gate
+
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: 2026-05-07
+**Feature**: [spec.md](../spec.md)
+
+## Content Quality
+
+- [X] No implementation details (languages, frameworks, APIs)
+- [X] Focused on user value and business needs
+- [X] Written for non-technical stakeholders
+- [X] All mandatory sections completed
+
+## Requirement Completeness
+
+- [X] No [NEEDS CLARIFICATION] markers remain
+- [X] Requirements are testable and unambiguous
+- [X] Success criteria are measurable
+- [X] Success criteria are technology-agnostic (no implementation details)
+- [X] All acceptance scenarios are defined
+- [X] Edge cases are identified
+- [X] Scope is clearly bounded
+- [X] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [X] All functional requirements have clear acceptance criteria
+- [X] User scenarios cover primary flows
+- [X] Feature meets measurable outcomes defined in Success Criteria
+- [X] No implementation details leak into specification
+
+## Notes
+
+- All items pass. Spec is ready for `/speckit-plan`.