Add a make package target for versioned Linux CLI release tarballs

Bundles deck-engine, interpreter-cli, run-engine.sh/run-interpreter.sh,
img/, i18n/, LICENSE, README.md, and docs/reading.md into
dist/deck-in-a-dash-<version>-linux-<arch>.tar.gz. Version defaults to
the current git tag (vX.Y.Z), falling back to a 0.0.0-dev+<sha>
placeholder when untagged

README.md

@@ -53,7 +53,8 @@ interpreter/                     Separate module + binary (dist/interpreter-cli)
                                   --format text|html|json and --lang en|de for
                                   its own output too (see CLAUDE.md).
 docs/                            Architecture/dataflow diagrams, input/output format reference.
-Makefile                         Single root Makefile, builds both engine/ and interpreter/.
+Makefile                         Single root Makefile, builds both engine/ and
+                                  interpreter/, and packages a release (`make package`).
 ```
 
 See [`CLAUDE.md`](CLAUDE.md) for the detailed architecture and the sharp
@@ -69,6 +70,10 @@ struct format reference
 make          # -> dist/deck-engine, dist/interpreter-cli, dist/img/, dist/i18n/,
               #    dist/run-engine.sh, dist/run-interpreter.sh, dist/user.properties
 make test     # builds and runs engine/tests/smoke_test.c and interpreter/tests/*_test.c
+make package  # -> dist/deck-in-a-dash-<version>-linux-<arch>.tar.gz, a
+              #    self-contained release bundle (binaries, scripts, img/, i18n/,
+              #    LICENSE, docs) - version from the current git tag, or
+              #    VERSION=1.2.3 make package to override
 ```
 
 Requires only a C99 compiler and `make` — no other dependencies.