fix(tui): hide initial instruction sync

[opencode-agent]

Summary

• mark the first durable instruction value sync as baseline-only live metadata
• keep the TUI from rendering that baseline sync as an "Instructions updated" message
• continue rendering genuine mid-session instruction changes

Root cause

The value-delta instruction sync introduced in #36254 persists the initial baseline through the same session.instructions.updated event used for later chronological changes. The model request correctly places those initial values in its system instructions, but the TUI treated every live sync event as a chronological update.

Tests

• bun test test/session-runner.test.ts (packages/core)
• bun test test/cli/tui/data.test.tsx (packages/tui)
• bun typecheck (packages/core)
• bun typecheck (packages/tui)