chore: update maintainer info and project metadata

- Change author to Sunbeam Studios
- Remove GitHub-specific files (.github/, renovate, README.template)
- Remove .env.example (replaced by .envrc workflow)
- Replace Makefile with justfile
- Update CHANGELOG with v1.0.0 fork notes
- Update Cargo.toml homepage to sunbeam.pt

justfile

@@ -0,0 +1,27 @@
+check:
+    cargo check --all-targets
+
+doc:
+    cargo doc --open
+
+fmt:
+    cargo fmt
+
+lint:
+    cargo clippy --all-targets
+
+publish:
+    cargo publish --registry sunbeam
+
+test:
+    cargo test --no-fail-fast
+
+test-cover:
+    cargo llvm-cov
+
+test-examples:
+    #!/usr/bin/env bash
+    for example in $(ls examples/*.rs | sed 's/examples\/\(.*\)\.rs/\1/'); do
+        echo "Running $example"
+        cargo run --example "$example"
+    done