fix(drive): render screenshots locally

[kitlangton]

What

Make Drive own screenshot rendering. OpenCode now exposes terminal frame capture over the simulation bridge, while opencode-drive converts that frame to PNG and writes it into the active instance generation's media directory.

Before / After

Before: ui.screenshot crossed the simulation RPC boundary, so OpenCode's simulation package had to carry Canvas, fonts, and PNG rendering code. That coupled production OpenCode artifacts to Drive-only capture behavior.

After: Drive sends ui.capture, renders the returned RGBA frame locally, and writes the PNG itself. Named, visible, direct-endpoint, scripted, and restarted instances all resolve screenshots to the correct media generation.

How

• Removes ui.screenshot from Drive's embedded OpenCode simulation protocol and keeps it as a Drive-level command.
• Adds local captured-frame rendering and a screenshot-specific Effect error.
• Persists each TUI's media directory in its runtime manifest and resolves CLI screenshots by active UI endpoint.
• Extends renderer coverage for RGBA alpha, braille glyphs, and heavy vertical box continuity.

Scope

• No historical screenshot RPC wire compatibility is retained.
• Release target selection (latest, next, exact versions/tags, and --dev) remains separate work.

Testing

• bun run check
• bun run test
• bun run release:validate
• CLI integration coverage for named, nameless visible, direct endpoint, scripted, and post-restart screenshots

Flow

sequenceDiagram
  participant Caller
  participant Drive
  participant OpenCode
  participant Media
  Caller->>Drive: ui.screenshot(name)
  Drive->>OpenCode: ui.capture
  OpenCode-->>Drive: captured RGBA frame
  Drive->>Drive: render PNG
  Drive->>Media: write active generation/name.png
  Media-->>Caller: screenshot path

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