fix: break-C — install-hooks no-ops without git; web image builds @mosaicstack/web

install-hooks.mjs hard-failed (exit 1) in environments without a git
binary — e.g. the docker image builds, which have no git and no repo.
Hook installation is meaningless there; skip with a warning instead.

docker/web.Dockerfile filtered @mosaic/web, but the package is named
@mosaicstack/web, so the image build compiled nothing.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01ESFAnh2t9HmLwng8oW95St

docker/web.Dockerfile

@@ -10,7 +10,7 @@ COPY apps/web/package.json ./apps/web/
 COPY packages/ ./packages/
 RUN pnpm install --frozen-lockfile
 COPY . .
-RUN pnpm --filter @mosaic/web build
+RUN pnpm --filter @mosaicstack/web build
 
 FROM base AS runner
 WORKDIR /app