feat(lab-03): complete Phase 4 - Compute & EC2 lab

Phase Plans (5 files):
- 04-RESEARCH.md: Domain research on Docker limits, healthchecks, EC2 parallels
- 04-VALIDATION.md: Success criteria and validation strategy
- 04-01-PLAN.md: Test infrastructure (RED phase)
- 04-02-PLAN.md: Diátxis documentation
- 04-03-PLAN.md: Infrastructure implementation (GREEN phase)

Test Scripts (6 files, 1300+ lines):
- 01-resource-limits-test.sh: Validate INF-03 compliance
- 02-healthcheck-test.sh: Validate healthcheck configuration
- 03-enforcement-test.sh: Verify resource limits with docker stats
- 04-verify-infrastructure.sh: Infrastructure verification
- 99-final-verification.sh: End-to-end student verification
- run-all-tests.sh: Test orchestration with fail-fast
- quick-test.sh: Fast validation (<30s)

Documentation (11 files, 2500+ lines):
Tutorials (3):
- 01-set-resource-limits.md: EC2 instance types, Docker limits syntax
- 02-implement-healthchecks.md: ELB health check parallels
- 03-dependencies-with-health.md: depends_on with service_healthy

How-to Guides (4):
- check-resource-usage.md: docker stats monitoring
- test-limits-enforcement.md: Stress testing CPU/memory
- custom-healthcheck.md: HTTP, TCP, database healthchecks
- instance-type-mapping.md: Docker limits → EC2 mapping

Reference (3):
- compose-resources-syntax.md: Complete deploy.resources reference
- healthcheck-syntax.md: All healthcheck parameters
- ec2-instance-mapping.md: Instance type mapping table

Explanation (1):
- compute-ec2-parallels.md: Container=EC2, Limits=Instance Type, Healthcheck=ELB

Infrastructure:
- docker-compose.yml: 5 services (web, app, worker, db, stress-test)
  All services: INF-03 compliant (cpus + memory limits)
  All services: healthcheck configured
  EC2 parallels: t2.nano, t2.micro, t2.small, t2.medium, m5.large
- Dockerfile: Alpine 3.19 + stress tools + non-root user

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

labs/lab-03-compute/how-to-guides/custom-healthcheck.md

@@ -0,0 +1,120 @@
+# How-to: Scrivere Healthchecks Personalizzati
+
+Come creare healthchecks custom per diversi tipi di servizi.
+
+## Pattern Comuni
+
+### HTTP Healthcheck
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "curl -f http://localhost/health || exit 1"]
+  interval: 15s
+  timeout: 3s
+  retries: 3
+```
+
+### TCP Port Check
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "nc -z localhost 8080 || exit 1"]
+  interval: 10s
+  timeout: 2s
+  retries: 3
+```
+
+### File Existence Check
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "test -f /var/run/app/ready || exit 1"]
+  interval: 5s
+  timeout: 1s
+  retries: 5
+```
+
+### Database Connection
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "mysqladmin ping -h localhost || exit 1"]
+  interval: 10s
+  timeout: 5s
+  retries: 5
+```
+
+### Redis Check
+
+```yaml
+healthcheck:
+  test: ["CMD", "redis-cli", "ping"]
+  interval: 10s
+  timeout: 3s
+  retries: 3
+```
+
+### Python Script Check
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "python /app/healthcheck.py || exit 1"]
+  interval: 30s
+  timeout: 10s
+  retries: 3
+```
+
+## Best Practices
+
+### 1. Check Leggeri
+```yaml
+# ✓ GOOD - pagina leggera
+test: ["CMD", "wget", "--spider", "-q", "http://localhost/health"]
+
+# ✗ AVOID - pagina pesante
+test: ["CMD", "wget", "--spider", "-q", "http://localhost/big-data"]
+```
+
+### 2. Timeout Appropriati
+```yaml
+# ✓ GOOD - timeout proporzionato all'interval
+interval: 10s
+timeout: 3s
+
+# ✗ AVOID - timeout troppo lungo
+interval: 10s
+timeout: 30s  # Riduce frequenza dei check
+```
+
+### 3. Retries Adeguati
+```yaml
+# ✓ GOOD - più retries per servizi lenti (database)
+healthcheck:
+  retries: 5
+
+# ✓ GOOD - meno retries per servizi veloci (web)
+healthcheck:
+  retries: 3
+```
+
+## Debugging
+
+### Testare manualmente
+```bash
+docker exec lab03-web wget --spider -q http://localhost/health
+echo $?  # 0 = success, !0 = failure
+```
+
+### Vedere log healthcheck
+```bash
+docker inspect lab03-web --format '{{range .State.Health.Log}}{{.Output}} {{end}}'
+```
+
+### Reset health status
+```bash
+docker restart lab03-web
+```
+
+## Vedi Anche
+- Tutorial: Implementare Healthchecks
+- Reference: Healthcheck Syntax