chore: add SPDX copyright headers and update license year

Add `// Copyright Sunbeam Studios 2026` and `// SPDX-License-Identifier:
Apache-2.0` headers to all source files missing them. Update LICENSE
copyright year, Dockerfile copyright header, and .dockerignore for new
project structure (lean4/, docs/, training artifacts).

Signed-off-by: Sienna Meridian Satterwhite <sienna@sunbeam.pt>

.dockerignore

@@ -2,4 +2,31 @@ target/
 .git/
 .gitignore
 *.md
+
+# Lean 4 proofs
+lean4/
+
+# Paper / docs
+docs/
+
+# Training data, datasets, artifacts
+*.bin
+*.jsonl
+models/
+.fastembed_cache/
+
+# burn training artifacts (checkpoints, experiment logs)
+src/ensemble/gen/scanner_artifacts/
+src/ensemble/gen/ddos_artifacts/
+
+# Dev / CI files
 certs/
+.github/
+.vscode/
+.idea/
+.claude/
+scripts/
+infrastructure/
+*.swp
+*.swo
+*~