gateway: agent-scoped "Recent runs" table with user, model and time

[Evanfeenstra]

Problem

On /agents/:name the Recent runs table was derived from /histogram/cost?dimension=run-id, which has no agent filter and sorts series by spend. So selecting canvas-agent showed every agent's runs (repo-agent, logs-agent, …), ranked by cost, and the run you had just triggered was nowhere near the top.

Fix

Backend — new GET /_plugin/agents/:name/runs?window=&limit=&offset= (agentruns.go), dispatched from the existing /_plugin/agents/ subtree next to <name>/spend:

• one row per run-id, scoped by metadata.agent-name, newest last_seen first (ties by run id for stable polling)
• per run: user_id, models (most-used first), total_cost, total_tokens, request_count, first_seen, last_seen
• total = run count before paging, so the UI can say "showing 50 of 120"
• timestamps compared as parsed times, not strings (RFC3339Nano trims trailing zeros, which misorders …:00Z vs …:00.5Z lexicographically)
• 404 without a logstore, 502 on upstream failure, 400 on bad window/limit — same contract as the sibling routes

UI — useAgentRuns hook (30s poll, the by-agent cadence). The table now shows:

Run	User	Model	Spend	Calls	Last call
uuid, ellipsized at 200px, full id on hover	first 8 chars, links to /people/:id, full id on hover	most-used model, +N pill listing the rest on hover			relative ("14m ago"), absolute on hover

Also: the cost chart now passes agent_name= so the server filters it (the hook already supported this), replacing the client-side series filter and the stale "phase-8 limitation" comment.

Tests

• agentruns_test.go: scoping (another agent's run must not leak), newest-first order, models by call count, user from the first stamped row, orphan rows without run-id skipped, sub-second ordering, paging, 400/404/502.
• go test ./internal/adminapi/ green; make tygo regenerated types.ts; tsc -b --noEmit and vite build clean.
• Rendered against a Node mock of the gateway routes (no real Bifrost yet): rows truncate/link/pill as described at 1280px; no console errors from the page.