chore: rename project from gosearch to kafka

A search engine named after a man who proved answers don't exist.

Renamed everywhere user-facing:
- Brand name, UI titles, OpenSearch description, CSS filename
- Docker service name, NixOS module (services.kafka)
- Cache key prefix (kafka:), User-Agent strings (kafka/0.1)
- README, config.example.toml, flake.nix descriptions

Kept unchanged (internal):
- Go module path: github.com/ashie/gosearch
- Git repository URL: git.ashisgreat.xyz/penal-colony/gosearch
- Binary entrypoint: cmd/searxng-go

Dockerfile

@@ -11,17 +11,17 @@ RUN go mod download
 
 # Copy source and build
 COPY . .
-RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /gosearch ./cmd/searxng-go
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /kafka ./cmd/searxng-go
 
 # Runtime stage
 FROM alpine:3.21
 
 RUN apk add --no-cache ca-certificates tzdata
 
-COPY --from=builder /gosearch /usr/local/bin/gosearch
-COPY config.example.toml /etc/gosearch/config.example.toml
+COPY --from=builder /kafka /usr/local/bin/kafka
+COPY config.example.toml /etc/kafka/config.example.toml
 
 EXPOSE 8080
 
-ENTRYPOINT ["gosearch"]
-CMD ["-config", "/etc/gosearch/config.toml"]
+ENTRYPOINT ["kafka"]
+CMD ["-config", "/etc/kafka/config.toml"]