2.0.0: changelog and skill docs for slugs and environments

Claude-Session: https://claude.ai/code/session_01SMCvdwDmuxoaqGgvGBLk1V

CHANGELOG.md

@@ -1,5 +1,38 @@
 # Changelog
 
+## 2.0.0
+
+Breaking change — major bump, required by the backend environments release.
+Every project now has exactly two environments, `staging` and `prod`, and the
+SDK key passed as `projectKey` decides which one the player belongs to. The
+environment never appears in the client API: it is resolved at login and
+carried inside the access and refresh tokens. Tokens issued before this
+release have no environment claim and are rejected with 401, so the first call
+after the backend upgrade refreshes, fails, clears the token store and emits
+`'signed-out'` to every `onAuthStateChange` listener. Log the player in again
+with `client.auth.loginWithDevice()` / `loginWithCustom()`.
+
+Quests, scenarios and offers are addressed by their slug instead of their id,
+because ids differ between staging and prod while slugs are stable. Renamed
+accordingly: `Quest.id` is now `Quest.slug`, `client.quests.claim()` takes a
+quest slug, `reportProgress()` resolves to the slugs of the completed quests
+(`ReportQuestProgressResponse.completedQuestSlugs`),
+`client.stores.purchase(storeSlug, offerSlug, options?)` takes an offer slug
+and `OfferHandle` carries a `slug` alongside its `id`,
+`QuestMetrics.purchaseOffer(offerSlug)` builds its metric from the offer slug,
+and every scenario-scoped type exposes `scenarioSlug` instead of `scenarioId` —
+`PendingEffect`, `ScenarioCompletedEffect`, `ScenarioFailedEffect`, the battle
+pass requests and `client.battlePass.getProgress(scenarioSlug, nodeId)`.
+`offer.buy()` is unchanged; it now binds the slug for you. Leaderboards, items
+and stores already used slugs and are untouched.
+
+Also shipped here, previously committed but never published: the effects client
+reconciles against every `GET /sdk/v1/scenarios/pending` response, so a run
+that disappears server-side (finished elsewhere, expired after a promote) now
+emits `onScenarioCompleted` instead of lingering; and `run_not_active` joins
+`unknown_run` and `run_expired` as a terminal rejection that drops the run and
+emits `onScenarioFailed`.
+
 ## 1.0.0
 
 - Scenario execution moved server-side. The SDK no longer walks a local DAG