Project 2 PR 1 (add libs/mofa-metrics crate with store, types, and HTTP/WS server)

[AdityaShome]

Changes

New standalone crate libs/mofa-metrics providing the core data layer for real time pipeline observability. Zero Makepad dependency, will be added in later prs.
Closes: #14

Files

File	Purpose
libs/mofa-metrics/Cargo.toml	Dependencies: axum (+ws), tokio, serde, parking_lot, futures, tower-http
src/types.rs	AgentState, AgentStatus, PipelineTrace, SystemSnapshot, MetricEvent
src/store.rs	Arc<MetricsStore> with dirty-flag tracking, ring-buffered traces/snapshots, broadcast
src/server.rs	axum HTTP server (4 REST endpoints + WebSocket), background tokio task
src/lib.rs	Module declarations and re-exports
Cargo.toml (root)	Added libs/mofa-metrics to workspace members

API

Endpoint	Description
GET /api/agents	All node statuses
GET /api/agents/{id}	Single node status
GET /api/metrics	Latest system snapshot
GET /api/pipeline	Recent pipeline traces
WS /ws	Real-time MetricEvent stream

Tests

5 unit tests covering dirty flag semantics, agent upsert, ring buffer caps, and snapshot ordering.