Phase 0: project scaffold and build pipeline

Go module (codeberg.org/mix/selfpost), two command skeletons (panel,
selfpost-backup) sharing internal/buildinfo for the -ldflags version stamp,
Makefile (static CGO_ENABLED=0 build), AGPL-3.0 LICENSE, README skeleton and
.gitattributes forcing LF (container scripts must not get CRLF).

Verified on the dev server: go vet clean, make build produces statically
linked binaries, version stamping works.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -1 +1,9 @@
+# Development-only material (secrets, server access notes) — never published.
 dev/
+
+# Build artifacts (binaries are built on the dev server, not committed).
+/bin/
+*.exe
+
+# Local Go caches / test output, if ever present.
+*.out