Fix OpenCode focus restore after replay gaps

[danshapiro]

Summary

• recover visible restored OpenCode panes when viewport hydration hits replay_window_exceeded by retiring the stale PTY before restored create
• add a red/green lifecycle test for the focus/activation path
• update the OpenCode restore research note with the production log evidence and repair policy
• remove the unused RestoreFallbackAttempt import that was failing lint

Verification

• npm run lint (exit 0; existing warnings remain)
• npm run test:vitest -- test/unit/client/components/TerminalView.lifecycle.test.tsx --run
• npm run test:vitest -- test/e2e/opencode-startup-probes.test.tsx --run

Base

This PR targets dev because the focus repair depends on the current OpenCode resilience integration stack already present there. A clean cherry-pick onto origin/main conflicts in TerminalView.tsx and the research note does not exist on origin/main yet.

[danshapiro]

Superseded by main-targeted replacements for the parity rebuild.

Verified coverage:

• Fix OpenCode replay-gap restore on main #348 carries the OpenCode visible viewport replay-gap repair and focused /home/user/code/freshell/src/components/TerminalView.tsx / /home/user/code/freshell/test/unit/client/components/TerminalView.lifecycle.test.tsx coverage onto main.
• Fix OpenCode replay-gap restore on main #348 carries the restore-contract note on main in /home/user/code/freshell/docs/lab-notes/2026-04-20-coding-cli-session-contract.md; the detailed dev research note is no longer a reason to keep a dev-target carrier open.
• Fix fresh-agent resume pane repair #354 carries the separate fresh-agent resume-pane repair for the main rebuild.

The only #346-only delta left is a one-line unused RestoreFallbackAttempt import removal in /home/user/code/freshell/src/store/panesSlice.ts on current dev. That is a dev-stack cleanup, not a main-parity payload, so this stale dev-target PR can be closed.