feat(tui): add internal debug frames

[kitlangton]

Summary

• add an internal/debug-only TUI fixture transport for rendering named static frames through the real TUI sync and session rendering path
• select fixture files and frames externally with --debug-scenario and --debug-frame; debug frames require --pure and do not start the normal worker/server transport
• add canonical subagent-lifecycle frames for foreground running, active background, retrying, failed, and completed subagent states
• validate fixtures with Effect Schema and fail closed for mutation requests against static frames

Usage

bun run dev --debug-scenario src/cli/cmd/tui/debug/fixtures/subagent-lifecycle.json --debug-frame running --pure
bun run dev --debug-scenario src/cli/cmd/tui/debug/fixtures/subagent-lifecycle.json --debug-frame active-background --pure
bun run dev --debug-scenario src/cli/cmd/tui/debug/fixtures/subagent-lifecycle.json --debug-frame retrying --pure
bun run dev --debug-scenario src/cli/cmd/tui/debug/fixtures/subagent-lifecycle.json --debug-frame failed --pure
bun run dev --debug-scenario src/cli/cmd/tui/debug/fixtures/subagent-lifecycle.json --debug-frame completed --pure

Design Boundaries

• Internal/debug-only initially; this is not a normal end-user workflow.
• Static named frames only in this PR. Playback and stepping are intentionally deferred.
• Fixtures describe rendered state (text, tool, and subagent parts); the transport compiler generates SDK-shaped sessions/messages/status responses.
• Renderer components remain unaware of debug mode.
• This PR is stacked above fix(tui): keep retry attempt before message #30275 because its canonical frames demonstrate the subagent rendering and wrap fixes in fix(tui): clarify inline subagent rows #30051, fix(tui): keep background marker with subagent label #30271, and fix(tui): keep retry attempt before message #30275; retarget to dev after the lower stack lands.

Verification

• bunx prettier --check src/cli/cmd/tui/thread.ts src/cli/cmd/tui/debug/frame.ts test/cli/tui/debug-frame.test.ts
• bun run test -- test/cli/tui/inline-tool-wrap-snapshot.test.tsx test/cli/tui/debug-frame.test.ts (14 pass, 6 snapshots)
• bun typecheck from packages/opencode
• pre-push bun turbo typecheck
• live cellshot renders for running, active-background, retrying, failed, and completed frames; narrow retry render verifies status-prefix wrapping
• confirmed running without --pure is rejected
• git diff --check

Scoped oxlint cannot currently run because the existing .oxlintrc.json on the base branch is rejected before source analysis due to duplicate/invalid options.typeAware placement.