Add gift clause rule for free gift encounters

When enabled, in-game gift Pokemon (starters, trades, fossils) do not
count against a location's encounter limit. Both a gift encounter and
a regular encounter can coexist on the same route, in any order.

Persists encounter origin on the Encounter model so the backend can
exclude gift encounters from route-lock checks bidirectionally, and the
frontend can split them into a separate display layer that doesn't lock
the route for regular encounters.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/types/game.ts

@@ -79,6 +79,7 @@ export interface Encounter {
   faintLevel: number | null
   deathCause: string | null
   isShiny: boolean
+  origin: string | null
   caughtAt: string
 }
 

frontend/src/types/rules.ts

@@ -2,6 +2,7 @@ export interface NuzlockeRules {
   // Core rules (affect tracker behavior)
   duplicatesClause: boolean
   shinyClause: boolean
+  giftClause: boolean
   pinwheelClause: boolean
   levelCaps: boolean
 
@@ -19,6 +20,7 @@ export const DEFAULT_RULES: NuzlockeRules = {
   // Core rules
   duplicatesClause: true,
   shinyClause: true,
+  giftClause: false,
   pinwheelClause: true,
   levelCaps: false,
 
@@ -55,6 +57,13 @@ export const RULE_DEFINITIONS: RuleDefinition[] = [
       'Shiny Pokémon may always be caught, regardless of whether they are your first encounter.',
     category: 'core',
   },
+  {
+    key: 'giftClause',
+    name: 'Gift Clause',
+    description:
+      "In-game gift Pokémon (starters, trades, fossils) do not count against a location's encounter limit.",
+    category: 'core',
+  },
   {
     key: 'pinwheelClause',
     name: 'Pinwheel Clause',