fix: Dockerfile uses thevlang/vlang:alpine container (pre-built V)

Building V from source on Alpine fails due to C function
redefinition (musl libc). Use the official V Alpine container
which has a pre-built, compatible V compiler.

Dockerfile

@@ -1,20 +1,12 @@
-# ── Build stage: compile ntfy-bridge from source ──────────────────────────
+# ── Build: use official V container to compile ────────────────────────────
-FROM alpine:3.20 AS builder
+FROM thevlang/vlang:alpine AS builder
-
-RUN apk add --no-cache gcc musl-dev git make
-
-# Build V from source, pinned to V 0.5.2 commit
-RUN git clone https://github.com/vlang/v /opt/v
-WORKDIR /opt/v
-RUN git checkout 45ae01d23168b6372f734eeb38a77360bbcf184a
-RUN make
 
 # Copy project source and build
 WORKDIR /src
 COPY . .
-RUN /opt/v/v -prod -o /ntfy-bridge .
+RUN v -prod -o /ntfy-bridge .
 
-# ── Runtime stage: minimal image ───────────────────────────────────────────
+# ── Runtime: minimal image ────────────────────────────────────────────────
 FROM alpine:3.20
 
 RUN apk add --no-cache ca-certificates tzdata curl