chore(qa): Final Wave cleanup — resolve lint findings from F2 review

Production code (all findings cleared):
- GenerationHistory: drop unused fetchProHistory(userId) param,
  change let activeId to const
- InitiativeTracker: remove write-only currentSessionName state
- NotesPanel: remove unused isLoading flag
- Open5eReference: drop unused getCachedTranslation/setCachedTranslation
  imports; use fetchTranslation result directly instead of re-lookup
- ai/openrouter.ts: drop unused z + Monster imports; attach cause to
  rethrown AbortError
- ai/kimi.ts: drop unused z import
- api/dm/ai/generate.ts: annotate best-effort counter increment catch
- api/dm/ai/history.ts: drop unused sql import

Test files (trivial fixes; ~70 mock-related `as any` errors remain as
pre-existing tech debt across api test mocks):
- translation-client: drop unused MockBroadcastChannel _name param and
  unused getCachedTranslation destructure
- open5e-types: eslint-disable for the intentional type-test aliases
- {notes,initiative}-api: remove unused mockUser2 placeholder
- {notes,initiative,translate,history}-api: let mockDb -> const mockDb
- ai-generate-api: wrap deliberate `var` mock decls in eslint-disable
  with comment explaining vi.mock hoisting requirement

Verification: tsc 0 errors, vitest 339/339, lint 81 -> 70 errors
(production code fully clean; remaining errors are test-mock as-any
patterns from Waves 5-6).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/open5e-types.test.ts

@@ -5,6 +5,7 @@ import type { Monster, Spell } from "../src/lib/open5e/client";
 // If a listed key is missing from the interface, TypeScript will error at compile time.
 type AssertKeys<T, K extends keyof T> = K;
 
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 type _MonsterHasAllFields = AssertKeys<
   Monster,
   | "name"
@@ -34,6 +35,7 @@ type _MonsterHasAllFields = AssertKeys<
   | "condition_immunities"
 >;
 
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 type _SpellHasAllFields = AssertKeys<
   Spell,
   | "name"