Adds a read-only, host-side usage indicator to the Share compute card so
you can see when someone (or your own agent) is using the compute this
machine is sharing, and where it's coming from.
- new read-only mesh_serving_usage Tauri command projects the serving
node's own routing_metrics (request/token counts, inflight, and the
local vs remote/endpoint attempt split). No new trust surface; stubbed
for non-mesh-llm builds.
- serving_usage_from_payload: pure, defensive extractor (missing fields
-> 0, so SDK shape drift degrades to 'no usage' not an error).
- deriveServingIndicator: pure label derivation. Distinguishes this
machine's OWN agents (local, shown softly) from another member
consuming this machine's compute (remote/endpoint -> the headline
'in use by another member' case).
- useMeshServingUsage: 4s poll, only while sharing.
- indicator rendered under the Share toggle status line.
- tests: 3 Rust (extractor local/remote/default), 7 TS (indicator label
table), e2e mock answers mesh_serving_usage + seed hook.
Verified live: firing a completion at the mesh API moves exactly the
fields the extractor reads (req/tokens/local_attempt), local-only traffic
correctly reads as not-a-remote-consumer.
Local-only exploration on the mesh-state-fix branch; not part of PR #2448.
