feat(vscode-ail-chat): toggle side panel — run history + pipeline steps

[AlexChesser]

Closes #167. Depends on #172 (#166).

Summary

• RunHistoryProvider — calls ail logs --format json --limit 100 to list past runs; no direct file access; refresh triggered by pipelineCompleted event from ChatViewProvider; openRunLog command calls ail log <runId> and opens output as a markdown document
• PipelineStepsProvider — parses active pipeline YAML (via the existing yaml dep); top-level steps only; sub-pipeline references render as single node with filename; error node on missing/malformed YAML or passthrough mode; openStep reveals the id: line in the editor
• toggleInfoPanel command — flips ail-chat.panelVisible context key; historyView and stepsView are gated on this key in package.json so they appear/disappear without disposal; toggle button in chat view title bar via menus["view/title"]
• ChatViewProvider wired: calls historyProvider.refresh() on pipelineCompleted, stepsProvider.refresh() on pipeline change
• All binary calls are injectable for unit testing; no direct file system access for log data

Test plan

• Toggle button in chat view title bar → Run History and Pipeline Steps panels appear; toggle again → disappear
• Run a prompt → Run History refreshes and shows the new entry
• Click a run entry → VS Code opens the run log as a markdown document
• Load a multi-step pipeline → Pipeline Steps shows top-level steps; click a step → YAML opens at that id: line
• Sub-pipeline reference → renders as single node with filename label
• Malformed YAML → error node, no throw
• No pipeline loaded → Pipeline Steps shows "No pipeline loaded" node
• npm test → 200 tests passing