Migrate cloudflare-ddns to Rust

Add Cargo.toml, Cargo.lock and a full src/ tree with modules and tests
Update Dockerfile to build a Rust release binary and simplify CI/publish
Remove legacy Python script, requirements.txt, and startup helper
Switch .gitignore to Rust artifacts; update Dependabot and workflows to
cargo
Add .env example, docker-compose env, and update README and VSCode
settings

Remove the old Python implementation and requirements; add a Rust
implementation with Cargo.toml/Cargo.lock and full src/ modules, tests,
and notifier/heartbeat support. Update Dockerfile, build/publish
scripts, dependabot and workflows, README, and provide env-based
docker-compose and .env examples.

Dockerfile

@@ -1,18 +1,13 @@
-# ---- Base ----
-FROM python:alpine AS base
+# ---- Build ----
+FROM rust:alpine AS builder
+RUN apk add --no-cache musl-dev
+WORKDIR /build
+COPY Cargo.toml Cargo.lock ./
+COPY src ./src
+RUN cargo build --release
 
-#
-# ---- Dependencies ----
-FROM base AS dependencies
-# install dependencies
-COPY requirements.txt .
-RUN pip install --user -r requirements.txt
-
-#
 # ---- Release ----
-FROM base AS release
-# copy installed dependencies and project source file(s)
-WORKDIR /
-COPY --from=dependencies /root/.local /root/.local
-COPY cloudflare-ddns.py .
-CMD ["python", "-u", "/cloudflare-ddns.py", "--repeat"]
+FROM alpine:latest AS release
+RUN apk add --no-cache ca-certificates
+COPY --from=builder /build/target/release/cloudflare-ddns /usr/local/bin/cloudflare-ddns
+CMD ["cloudflare-ddns", "--repeat"]