Document container build pattern and port navidrome (#192)

## Summary
- Add how-to guide (`docs/how-to/build-container-image.md`) covering the full container build workflow: directory layout, Dagger local builds, mise release task, and common patterns with links to existing containers
- Port navidrome from upstream `deluan/navidrome:0.60.3` to a custom three-stage build (`containers/navidrome/Dockerfile`) using Node + Go + Alpine
- Update navidrome deployment to use `registry.ops.eblu.me/blumeops/navidrome:v1.0.0`

## Deployment and Testing
- [x] `dagger call build --src=. --container-name=navidrome` builds successfully
- [ ] After merge: `mise run container-tag-and-release navidrome v1.0.0`
- [ ] After image published: `argocd app sync navidrome` and verify pod starts

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/192

containers/navidrome/Dockerfile

@@ -0,0 +1,52 @@
+# Navidrome music server
+# Three-stage build: UI (Node), backend (Go+taglib), runtime (Alpine)
+
+ARG NAVIDROME_VERSION=v0.60.3
+
+FROM node:22-alpine AS ui-build
+
+ARG NAVIDROME_VERSION
+RUN apk add --no-cache git
+
+RUN git clone --depth 1 --branch ${NAVIDROME_VERSION} \
+    https://forge.ops.eblu.me/eblume/navidrome.git /app
+
+WORKDIR /app/ui
+RUN npm ci
+RUN npm run build
+
+FROM golang:alpine3.22 AS build
+
+ARG NAVIDROME_VERSION
+RUN apk add --no-cache build-base git taglib-dev
+
+RUN git clone --depth 1 --branch ${NAVIDROME_VERSION} \
+    https://forge.ops.eblu.me/eblume/navidrome.git /app
+
+WORKDIR /app
+
+# Copy pre-built UI assets
+COPY --from=ui-build /app/ui/build /app/ui/build
+
+ENV CGO_ENABLED=1
+ENV CGO_CFLAGS_ALLOW="--define-prefix"
+
+RUN go build -tags=netgo \
+    -ldflags="-w -s -X github.com/navidrome/navidrome/consts.gitTag=${NAVIDROME_VERSION}" \
+    -o /navidrome .
+
+FROM alpine:3.22
+
+LABEL org.opencontainers.image.title=Navidrome
+LABEL org.opencontainers.image.description="Navidrome is a self-hosted music server and streamer"
+# Points to upstream canonical source, not the forge mirror used for builds
+LABEL org.opencontainers.image.source=https://github.com/navidrome/navidrome
+
+RUN apk add --no-cache ca-certificates tzdata taglib ffmpeg
+
+COPY --from=build /navidrome /usr/bin/navidrome
+
+EXPOSE 4533
+
+USER 65534
+CMD ["/usr/bin/navidrome"]