Add Woodpecker CI pipeline, make Dockerfile multi-stage

- Multi-stage Dockerfile: download Zig 0.15.2, build inside Docker
- .woodpecker/deploy.yml: Kaniko build + push + manifest update

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -1,4 +1,12 @@
+FROM alpine:3.21 AS builder
+RUN apk add --no-cache curl xz
+WORKDIR /zig
+RUN curl -fsSL https://ziglang.org/download/0.15.2/zig-x86_64-linux-0.15.2.tar.xz | tar xJ --strip-components=1
+WORKDIR /app
+COPY . .
+RUN /zig/zig build -Doptimize=ReleaseSafe
+
 FROM alpine:3.21
 RUN apk add --no-cache ffmpeg curl ca-certificates
-COPY zig-out/bin/transcribator /usr/local/bin/
+COPY --from=builder /app/zig-out/bin/transcribator /usr/local/bin/
 CMD ["transcribator"]