fix(tui): clarify inline subagent rows

[kitlangton]

Summary

• render completed inline subagents with a distinct ✓ state while retaining a readable elapsed-time detail row
• preserve the running subagent spinner and current-child activity line (↳ Read ...)
• keep launched background subagents active only while their child session is present in the non-idle session status map
• add blank-row boundaries around contiguous inline subagent groups while keeping adjacent subagents compact
• omit empty 0 toolcalls counts and pluralize non-zero toolcall counts correctly

Selected Rendering

⠇ Explore Task — Trace spacing while surrounding tools stay visible
  ↳ Read src/cli/cmd/tui/routes/session/index.tsx
✓ General Task — Answer directly (background)
  ↳ 501ms
✓ Explore Task — Inspect source (background)
  ↳ 1 toolcall · 501ms

Verification

• bunx prettier --check src/cli/cmd/tui/routes/session/index.tsx test/cli/tui/inline-tool-wrap-snapshot.test.tsx
• bun run test -- test/cli/tui/inline-tool-wrap-snapshot.test.tsx (7 pass, 6 snapshots)
• bun typecheck from packages/opencode
• bun turbo typecheck via the pre-push hook
• git diff --check
• Scoped oxlint is currently blocked before source analysis by the existing invalid duplicate options.typeAware configuration in .oxlintrc.json; no lint-config change is included here.

The deterministic internal TUI preview harness used while developing this change has been removed from this PR and will be designed separately as an internal/debug-only follow-up.

[kitlangton]

Fresh cellshot 0.7.0 captures after rebasing onto current dev. These were rendered with CommitMonoV143 so the live Braille spinner glyphs appear correctly in PNG output.

Completed subagent group

All completed rows, including background completions, retain the final duration line.

Running, completed, and background-active subagent groups between inline tools

The second active group demonstrates a background task whose parent call has returned while its child session is still busy; it remains a spinner row rather than displaying ✓. Completed background rows show their elapsed time consistently.

Mixed block and inline tool context

[opencode-agent]

⚠️ Blocking Beta Release

This PR cannot be merged into the beta branch due to: Merge conflicts with dev branch

Please resolve this issue to include this PR in the next beta release.