Observe filter bar and Slack onboarding split

This patch release unifies the Observe filter bar across Insights, Tools, and Logs views, rebuilds the assistant Slack install step into two clearer cards, and auto-enables MCP on toolsets attached to assistants.

Features

• Unified Observe filter bar #2616  - Unifies the Observe filter bar for Insights Tools and Logs Tools views; server, email, and type filters are now multi-select dropdowns with OR semantics. (Author: @alx-xo )
• Slack install step split into install + tokens cards #2735  - Rebuilds the assistant-onboarding Slack install step as two separate cards: an install card (workspace pick, install, Event Subscriptions Retry) followed by a tokens card. Copy rewritten for non-technical users, with the Event Subscriptions Retry step called out as the most common silent failure. (Author: @danielkov )

Bug fixes

• Auto-enable MCP on assistant-attached toolsets #2722  - Auto-enables MCP on toolsets when they are attached to an assistant, so the runtime can build a startup config without manual toggling. (Author: @danielkov )
• PostHog disposition person property #2728  - Tags users who sign up with disposition=assistants with a PostHog person property so the assistants feature flag can target them. (Author: @danielkov )