feat: add DM screen and battle organizer

[Daren9m]

What changed

• add a configurable DM screen with nested collapsible sections and hide/show controls
• support notes, monsters, spells, app shortcuts, auto-synced pinned references, and a focused initiative tracker element
• add a standalone battle organizer with initiative ordering, acting/next/on-deck callouts, rounds, HP and temporary HP, conditions, concentration, reactions, legendary actions, notes, and an event log
• add Markdown, JSON, print, and battle export workflows
• add a Run Battle handoff from configured encounters, carrying over party names/stats and individual monster instances
• add navigation, route metadata, persistence, and pure state helpers for both features

Why

DMs need one configurable command surface for session references and a dedicated live-combat workflow. The shared battle state lets the standalone organizer and DM-screen initiative element stay synchronized, while the encounter handoff removes duplicate setup at the table.

User impact

Users can prepare a reusable DM screen, launch generated encounters directly into initiative, and continue managing the same battle from either /battle or the embedded initiative tracker.

Validation

• npm run typecheck
• npm run lint
• npm test — 649 tests passed
• npm run build — static export completed successfully
• desktop and responsive local browser verification