fix(dash): give instances a real Ready status instead of a Running catch-all

[michaelroy-amd]

Summary

InstanceStatus had no Ready state, so merge_instance hardcoded every discovered instance to Running regardless of whether it had actually passed a readiness probe. Managed services with a "ready" record status, Lemonade endpoints (only ever built after a health probe), and Docker-discovered containers all collapsed into the same Running label, hiding real lifecycle differences from the TUI and any future readiness-aware consumer (e.g. chat endpoint selection).

Root Cause

rocm_dash_core::traits::merge_instance unconditionally set status: InstanceStatus::Running on every Instance it built, and InstanceStatus itself had no variant to represent "passed its readiness probe" as distinct from "process is up." Every discovery source (managed-service registry, Lemonade collector, Docker collector) therefore reported the same status label no matter what it actually knew about the endpoint's readiness.

Changes

• Add InstanceStatus::Ready and an is_serving() helper (Ready | Running) for call sites that only care about "is this actively serving."
• Add a status field to DiscoveredService so each discovery source reports what it actually knows; merge_instance now uses svc.status instead of a hardcoded Running.
• rocm-dash-daemon::registry::discovered_from_record maps a managed-service record's status string (ready/running/starting/recovering) to the matching InstanceStatus. "recovering" was previously dropped from the scrapeable set entirely (a bug relative to apps/rocm/src/main.rs's own "is this service live" checks, which treat recovering as live) — it's now scraped and mapped to Starting.
• rocm-dash-collectors::lemonade::lemonade_service builds as Ready since every call site only constructs it after a successful /api/v1/health probe.
• rocm-dash-collectors::docker has no readiness signal of its own, so Docker-discovered instances start Starting; rocm-dash-daemon::runner::run_loop promotes them to Ready on their first successful vLLM Prometheus scrape or Lemonade stats fetch (documented scope: this is the only readiness signal available for Docker-discovered instances).
• Add Ready arms to the exhaustive status_meta/status_role matches in crates/rocm-dash-tui/src/ui/tabs/instances.rs; switch the == InstanceStatus::Running equality checks in home.rs/dock.rs/launcher.rs to .is_serving().

Test Plan

• cargo build -p rocm-dash-core -p rocm-dash-collectors -p rocm-dash-daemon -p rocm-dash-tui
• cargo clippy -p rocm-dash-core -p rocm-dash-collectors -p rocm-dash-daemon -p rocm-dash-tui --all-targets --all-features -- -D warnings
• cargo test -p rocm-dash-core -p rocm-dash-collectors -p rocm-dash-daemon (all green, including 2 new tests: instance_status_ready_round_trips_as_lowercase_json, instance_status_is_serving_covers_ready_and_running_only, and discovered_from_record_maps_status_string_to_instance_status)
• cargo test -p rocm-dash-tui -- --test-threads=1 (543 + 16 + 5 tests green)

Relates to EAI-7350