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/reference/healthcheck-syntax.md

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+# Reference: Docker Compose Healthcheck Syntax
+
+Riferimento completo per la configurazione degli healthchecks.
+
+## Sezione healthcheck
+
+### Struttura Completa
+
+```yaml
+services:
+  service_name:
+    healthcheck:
+      test: ["CMD", "command", "arg1", "arg2"]
+      interval: 30s
+      timeout: 30s
+      retries: 3
+      start_period: 0s
+```
+
+## Parametri
+
+### test (Required)
+
+Comando da eseguire per verificare la salute.
+
+**Formato CMD:**
+```yaml
+test: ["CMD", "wget", "--spider", "-q", "http://localhost/health"]
+```
+
+**Formato CMD-SHELL:**
+```yaml
+test: ["CMD-SHELL", "curl -f http://localhost/ || exit 1"]
+```
+
+**Formato NONE:**
+```yaml
+test: ["NONE"]
+```
+Disabilita healthcheck ereditato dall'immagine.
+
+### interval
+
+Frequenza di esecuzione del test.
+
+```yaml
+interval: 5s       # Ogni 5 secondi
+interval: 10s      # Ogni 10 secondi
+interval: 30s      # Ogni 30 secondi (default)
+interval: 1m       # Ogni minuto
+```
+
+**Validità:**
+- Minimo: `1s` (1 secondo)
+- Massimo: Nessuno
+- Default: `30s`
+
+### timeout
+
+Tempo massimo per completare il test.
+
+```yaml
+timeout: 2s        # 2 secondi
+timeout: 5s        # 5 secondi (default)
+timeout: 30s       # 30 secondi
+```
+
+**Nota:** Se il test supera il timeout, conta come fallimento.
+
+### retries
+
+Numero di fallimenti consecutivi prima di marcare unhealthy.
+
+```yaml
+retries: 1         # 1 fallimento = unhealthy
+retries: 3         # 3 fallimenti = unhealthy (default)
+retries: 5         # 5 fallimenti = unhealthy
+```
+
+**Calcolo del tempo unhealthy:**
+```
+tempo_totale = (interval + timeout) × retries
+```
+
+Esempio con `interval: 10s, timeout: 5s, retries: 3`:
+- Check 1: 0s - 5s
+- Check 2: 10s - 15s
+- Check 3: 20s - 25s
+- Unhealthy dopo: 25s
+
+### start_period
+
+Grace period prima di contare retries verso unhealthy.
+
+```yaml
+start_period: 0s   # Nessun grace period (default)
+start_period: 5s   # 5 secondi di grace
+start_period: 10s  # 10 secondi di grace
+start_period: 30s  # 30 secondi di grace
+```
+
+**Comportamento:**
+- Durante `start_period`: Fallimenti non contano
+- Dopo `start_period`: `retries` inizi a contare
+
+## Esempi per Tipo di Servizio
+
+### HTTP Service (Nginx)
+
+```yaml
+healthcheck:
+  test: ["CMD", "wget", "--quiet", "--tries=1", "--spider", "http://localhost/"]
+  interval: 10s
+  timeout: 5s
+  retries: 3
+  start_period: 5s
+```
+
+### Database (PostgreSQL)
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "pg_isready -U postgres || exit 1"]
+  interval: 10s
+  timeout: 5s
+  retries: 5
+  start_period: 10s
+```
+
+### Cache (Redis)
+
+```yaml
+healthcheck:
+  test: ["CMD", "redis-cli", "ping"]
+  interval: 10s
+  timeout: 3s
+  retries: 3
+```
+
+### TCP Connection
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "nc -z localhost 8080 || exit 1"]
+  interval: 15s
+  timeout: 2s
+  retries: 3
+```
+
+### File Check
+
+```yaml
+healthcheck:
+  test: ["CMD-SHELL", "test -f /tmp/ready || exit 1"]
+  interval: 5s
+  timeout: 1s
+  retries: 5
+```
+
+## Stati di Salute
+
+### Ciclo di Vita
+
+```
+created → starting → healthy
+                ↓
+              unhealthy
+```
+
+**Transizioni:**
+
+| Da | A | Condizione |
+|----|---|------------|
+| created | starting | Container avviato con healthcheck |
+| starting | healthy | `retries` consecutivi passano |
+| starting | unhealthy | `retries` consecutivi falliscono (dopo start_period) |
+| healthy | unhealthy | `retries` consecutivi falliscono |
+| unhealthy | healthy | 1 check passa |
+
+### Ispezionare Stato
+
+```bash
+# Stato corrente
+docker inspect lab03-web --format '{{.State.Health.Status}}'
+# Output: healthy / unhealthy / starting
+
+# Exit code dell'ultimo check
+docker inspect lab03-web --format '{{.State.Health.ExitCode}}'
+# Output: 0 (success) o !0 (failure)
+
+### Vedi Anche
+- Tutorial: Implementare Healthchecks
+- How-to: Custom Healthcheck