fix(timeline): move meetings to top timeline

[ComputelessComputer]

Replace the default sidebar timeline with a top meeting timeline, add 30-minute duration bars with pan and zoom support, and keep custom sidebars intact.

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Note

Medium Risk
Large UI shell change plus session delete/open and calendar-ignore paths on the new timeline; sidebar lock/unmount behavior was adjusted for custom tabs.

Overview
Moves the default meetings experience from the left sidebar into a horizontal top carousel (TopMeetingTimeline) under tab chrome when the sidebar is expanded and the tab is not onboarding, devtool, or a custom-sidebar type (calendar, settings, etc.).

Layout & chrome: ClassicMainBody conditionally renders the top timeline and relocates ToastArea to a floating corner; ClassicMainSidebar no longer shows LeftSidebar for the default case—only devtool or custom-sidebar tabs. The sidebar toggle uses top-panel icons and “Toggle timeline” when that mode applies.

Timeline behavior: New helpers default missing/invalid ends to 30 minutes (normalizeEndMs) and derive session spans from transcript rows (buildSessionRecordingRanges). Cards support open/delete/ignore flows, previews, a Today jump chip, and horizontal scroll (including vertical wheel → horizontal). Calendar events skip all-day rows; future events only; session/event deduping by tracking id.

Supporting fixes: showNativeContextMenu extracted for reuse; useCustomSidebarEffect cleans up on unmount; session preview omits blank participant names; tests updated for the new layout.

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