feat(sidebar): filter tasks by workspace type

[MattPua]

Problem

No way to filter the tasks sidebar by where a task runs. When you have a mix of worktree, local, and cloud tasks, the list gets noisy and there's no way to narrow it to just the type you care about.

Changes

• Added a Task type section to the tasks filter menu with multi-select checkboxes for Worktree, Local, and Cloud.
• Classification uses Workspace.mode, falling back to the cloud run environment when there's no local workspace.
• Tasks with an unknown mode always stay visible so nothing silently disappears.
• Selection is persisted (defaults to all types enabled) and visible to everyone.

Unchecking all three leaves only unknown-mode tasks visible (literal filter semantics).

How did you test this?

• @posthog/core + @posthog/ui typecheck clean
• Added unit tests for filterByWorkspaceMode (4 cases) -- all pass via vitest
• biome lint clean on changed files, no noRestrictedImports

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 7e1d855.}