Add Grok goal and subagent support

[SDSLeon]

What changed

• bridge Grok goal lifecycle metadata into the shared goal UI, including pause, resume, and clear controls
• constrain long goal objectives so the composer dock truncates correctly
• normalize Grok background subagents into nested child timelines
• populate both the inline Subagent Result and right-panel transcript from Grok's final child output
• hide the redundant get-task-output transport row

Root cause

Grok emits provider-specific goal and subagent extension events. Its background spawn receipt can arrive before subagent_spawned, so the generic ACP mapper previously completed and discarded the parent correlation before the child result arrived.

Verification

• real Grok 4.5 Electron run: goal controls and truncation exercised
• real Grok 4.5 Electron run: final child marker shown inline and in the right panel; wait row absent
• pnpm exec vitest run src/supervisor/agents/grok/acpTransform.test.ts src/supervisor/agents/acp/canonicalMapping.test.ts src/supervisor/agents/grok/grok.test.ts
• pnpm run typecheck
• pnpm run lint
• pnpm run fmt:check
• pnpm run test (7,945 passed, 35 skipped)