fix(app): annotate showAvatar to break TS7022 circular inference

[graydawnc]

What

buildRows in MessageList.tsx declared showAvatar with no type. Under the app's tsconfig.json, TypeScript flags it TS7022 — "implicitly has type 'any' because it is referenced directly or indirectly in its own initializer" — from a circular control-flow inference through the Row union (row = { kind: 'msg', msg, showAvatar }). Pinning showAvatar: boolean (the type Row's msg variant already requires) breaks the cycle.

Why

The error has been latent since #265. It never gated anything because the app build runs esbuild via electron-vite (no type-check) and CI's e2e.yml has only unit (vitest) + e2e (playwright) jobs — no tsc step. So pnpm -C packages/app exec tsc --noEmit reported it but nothing enforced it. This clears the one outstanding type error so the app package type-checks clean.

How it connects

Pure type annotation on one local; no runtime/behaviour change. The value is identical (!prevMsg || prevMsg.role !== msg.role || prevMsg.role === 'system').

Test plan

• pnpm -C packages/app exec tsc --noEmit -p tsconfig.json — was 1 error (MessageList:128), now clean (exit 0), whole app package included.
• Adjacent suites unaffected (no behaviour change); unit + e2e continue to pass.

Coverage note: this class of error can't be guarded by a runtime test, and the repo currently runs no tsc job in CI, so nothing automatically prevents recurrence. Out of scope here; a separate change could add a typecheck gate (the app package now type-checks clean, so such a gate would pass).

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