Encounter templates: duplicate without wiping run state

[gwillish]

Allow a GM to duplicate an encounter definition as a clean template — without copying any in-progress session state.

Scope

• "Duplicate as Template" option in encounter library (context menu or swipe action)
• Creates a new EncounterDefinition with the same roster, player configs, and GM notes
• The duplicate has no associated session — starts fresh when run
• Original encounter and its session are unchanged

Depends on

• Phase 4 complete

Acceptance criteria

• Duplicate appears in library as a new entry with same name + " Copy" suffix
• Duplicate contains same adversary roster, players, GM notes
• Duplicate has no session — "Run Encounter" starts fresh
• Original unaffected