Add the initial mediamark app

Single Go binary serving the API and an embedded keyboard-first UI for
promoting fafflix titles into the cheeztv kids tree via hardlinks.

- internal/library: hardlink sync, idempotent re-runs, drift reporting,
  strict single-path-element name validation as the traversal guard
- internal/arr: minimal sonarr/radarr v3 client with a 60s list cache and
  a key-brokered poster proxy
- internal/auth: server-side Authentik group enforcement on every route
- internal/server: library JSON API, art proxy, health probes, SPA
- ui: two-tile landing page, fuzzy-filtered title list, detail panel
- Makefile, Dockerfile, .woodpecker pipelines, pre-commit config

Dockerfile

@@ -0,0 +1,21 @@
+FROM golang:1.25-alpine AS builder
+
+RUN apk add --no-cache git
+
+WORKDIR /build
+
+COPY go.mod ./
+RUN go mod download
+
+COPY . .
+
+ARG VERSION=dev
+RUN CGO_ENABLED=0 go build -ldflags="-s -w -X main.version=${VERSION}" -o mediamark ./cmd/mediamark
+
+FROM gcr.io/distroless/static-debian12:nonroot
+
+COPY --from=builder /build/mediamark /usr/local/bin/mediamark
+
+EXPOSE 8080
+
+ENTRYPOINT ["mediamark"]