[PAP-3154] Stop padding /live-runs by default (#4963)

## Summary
- Fix [PAP-3154](/PAP/issues/PAP-3154): the Sidebar's "Dashboard NN
live" badge showed a constant 50 in every company because `GET
/api/companies/:companyId/live-runs` was padding its response with up to
50 recent (non-live) heartbeat runs whenever the caller did not pass
`minCount`.
- Regression introduced by
[#4875](https://github.com/paperclipai/paperclip/pull/4875) (commit
`6445bef9`), which capped both `minCount` and `limit` at 50 with a
fallback of 50 for omitted values. The cap is correct for `limit` (real
unboundedness guard); for `minCount` it conflates "no padding" with "pad
to the cap".
- Default `minCount` to 0 so callers asking for "live runs" only get
actually-live runs unless they explicitly request padding
(`ActiveAgentsPanel` is the only caller that does). Keep `limit` capped
at 50 by default.

## Test plan
- [x] `pnpm exec vitest run
server/src/__tests__/agent-live-run-routes.test.ts` — 7/7 pass,
including new tests for the no-pad default and explicit padding.
- [x] `pnpm exec vitest run ui/src/components/Sidebar.test.tsx
ui/src/components/ActiveAgentsPanel.test.tsx
ui/src/api/heartbeats.test.ts` — 6/6 pass.
- [ ] Verify in dev: with ~8 truly-live runs in a company, the sidebar
Dashboard badge shows the real count (not 50).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/routes/agents.ts

@@ -2844,7 +2844,12 @@ export function agentRoutes(
     const companyId = req.params.companyId as string;
     assertCompanyAccess(req, companyId);
 
-    const minCount = readLiveRunsQueryInt(req.query.minCount, 50, 50);
+    // `minCount` is a padding floor for callers that want a minimum number of
+    // recent runs to render (e.g. dashboard cards). It must default to 0 so
+    // callers asking for "live runs" get only actually-live runs — otherwise
+    // every caller with no minCount param gets up to 50 historical runs
+    // padded in and renders bogus "live" counts.
+    const minCount = readLiveRunsQueryInt(req.query.minCount, 50, 0);
     const limit = readLiveRunsQueryInt(req.query.limit, 50, 50);
 
     const columns = {