Fix fresh-agent header cleanup and rename UX

[danshapiro]

Summary

• remove the unused FreshAgentContextMeter component and its obsolete unit test
• keep user-renamed fresh-agent pane titles visible alongside runtime metadata
• suppress redundant default fresh-agent labels when metadata already carries the directory/branch/context line

Verification

• npm run check
• npm run lint
• npm run test:e2e:chromium -- test/e2e-browser/specs/fresh-agent.spec.ts
• npm run test:vitest -- --run test/unit/client/components/panes/PaneHeader.test.tsx test/unit/client/components/panes/PaneContainer.test.tsx test/e2e/pane-header-runtime-meta-flow.test.tsx test/e2e/pane-activity-indicator-flow.test.tsx