feat(dashboard): maximize the Live View with Enter, restore with Esc

[ThomasK33]

What

Adds a maximize affordance to the read-only dashboard's Live View. Press Enter — from the session list or the focused Live View pane — to blow the selected session's Live View up to the full dashboard body (the session list is dropped); Esc restores the split view.

Behaviour

• Enter maximizes — from the list (jump straight from browsing to watching the selected session) or from the focused pane.
• Esc restores. Maximize is a modal layer that never mutates focus, so Esc returns you to whatever was focused underneath (list → list, pane → pane).
• While maximized: panning (↑/↓ h/j/k/l) and the z Overview toggle keep working; the header and footer stay; Tab/H/a are inert so it reads as a distinct mode.
• The maximized pane keeps the same right edge as the split view, so toggling never shifts the frame; it stays bordered (a borderless full-bleed pane read too much like "am I in my own shell?").

Design

Shipped after a prototype + a grilling session:

• A presentation affordance, not a domain concept — CONTEXT.md is unchanged (the Live View is still clipped/panned/overview to fit a pane per ADR 0006; only the pane size changes).
• Named maximize, not "zoom": it enlarges the viewport rather than magnifying content, and "zoom" is already the PRD's word for the z/Overview scale toggle.
• Modeled as an orthogonal maximized boolean (a modal layer), not a 4th focus value — its key target is identical to live.

Refactors (from a max-effort self-review)

• Extracted pane-dimension math into a tested paneLayout(termCols, termRows, maximized) helper beside listWidthFor, with a unit test pinning the right-edge-stays-put invariant across the toggle.
• Shared the pan and Overview key handling between the split and maximized input paths (handlePanKeys / toggleOverview).
• Pan resets on the maximize/restore toggle (matching every other geometry transition, avoiding a stale-pan dead keypress); Enter no-ops when no session is selected.

Verification

typecheck · lint · format · 1375 unit tests (incl. 3 new paneLayout tests) all green. Behaviour verified by hand against real sessions (the dashboard needs a real TTY; CI can't drive it).

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