refactor(infrastructure): [#301] Phase 4 - Extract ServiceTopology shared type

[josecelano]

Summary

Closes #301

This PR completes Phase 4 of the Docker Compose Topology Domain Model Refactoring by extracting a shared ServiceTopology type to formalize the architectural pattern discovered during cleanup.

Problem

After Phase 3 cleanup that removed unused fields from all ServiceContext types, we observed that all 5 types (TrackerServiceContext, GrafanaServiceContext, PrometheusServiceContext, CaddyServiceContext, MysqlServiceContext) now share identical fields:

pub ports: Vec<PortDefinition>
pub networks: Vec<Network>

This wasn't just coincidence - it represents a clear architectural pattern:

• Topology data (ports/networks) → needed for docker-compose.yml template (inter-service relationships)
• Configuration data (credentials, intervals) → injected via .env files (internal service config)

Solution

Extract a shared ServiceTopology type to make this pattern explicit:

#[derive(Serialize, Debug, Clone, PartialEq, Default)]
pub struct ServiceTopology {
    pub ports: Vec<PortDefinition>,
    pub networks: Vec<Network>,
}

All ServiceContext types now embed this with #[serde(flatten)] to maintain template compatibility (flat JSON structure).

Changes

New File

• service_topology.rs - Shared topology structure with documentation explaining the design rationale

Updated ServiceContext Types

All now use the embedded ServiceTopology pattern:

• TrackerServiceContext
• GrafanaServiceContext
• PrometheusServiceContext
• CaddyServiceContext
• MysqlServiceContext

API Changes

• Added ports() and networks() accessor methods to each ServiceContext
• Updated builder.rs to use accessor methods
• Updated all tests to use accessor methods

Testing

• All 2075 library tests pass
• All E2E tests pass (infrastructure lifecycle + deployment workflow)
• Pre-commit checks pass (linting, formatting, spell check, clippy)

Architecture Diagram

┌─────────────────────────────────────────────────────┐
│           ServiceContext (e.g., Tracker)            │
├─────────────────────────────────────────────────────┤
│  #[serde(flatten)]                                  │
│  pub topology: ServiceTopology                      │
│    ├── ports: Vec<PortDefinition>    ─────┐         │
│    └── networks: Vec<Network>         ────┼── JSON  │
│                                           │  flat   │
└───────────────────────────────────────────┴─────────┘
                        ↓
            docker-compose.yml.tera template

Related

• Epic: [Epic] Docker Compose Topology Domain Model Refactoring #287 - Docker Compose Topology Domain Model Refactoring
• Predecessor: [Refactor] Phase 3: Port Topology Template Integration (P3.4) #300 - Phase 3 Port Topology Template Integration
• Plan: docs/refactors/plans/docker-compose-topology-domain-model.md

[josecelano]

ACK 14a27e4