feat: per-service resource metrics dashboard endpoint

[yasinBursali]

Problem

• No API endpoint for per-service CPU, RAM, and disk metrics
• Dashboard cannot show resource usage breakdown by service
• Disk usage scanning is locked inside a nested function, preventing reuse

Proposed Solution

• Add GET /api/services/resources endpoint returning per-service metrics
• Fetch container stats from host agent, scan disk locally
• Separate cache TTLs: 20s for container stats, 60s for disk scans

Scope

• NEW dashboard-api/routers/resources.py
• dashboard-api/main.py — register router

[yasinBursali]

Implementation PR: #810

[yasinBursali]

Closing — issue filed on wrong repo.