feat(release): SemVer + ludicc --version, changesets, and x release

The project had no versioning discipline: 0 tags, no CHANGELOG, no way for the
compiler to report a version. Add a lightweight, native release flow.

- Versioning: SemVer, with VERSION as the single source of truth. `ludicc
  --version` (and `ludic --version`) read it at runtime — so a bump touches one
  file and never reseeds the compiler. `x version` reports it too.
- Changesets: one small Markdown file per user-facing change under changes/
  (bump level + type + summary; see changes/README.md). This replaces "remember
  to edit the changelog" with a mergeable artifact, no Node changeset tool.
- `x release [major|minor|patch] [--publish]`: fold the pending changesets into a
  new CHANGELOG.md section (grouped by type), bump VERSION, commit, and tag
  vX.Y.Z. The level defaults to the highest changeset bump. `--publish` also
  pushes and creates the Forgejo release with source + toolchain tarballs;
  tools/ci/forgejo_release.py is the small stdlib-Python HTTP glue for the
  release API (a native Http client is issue #6).

Seed the initial changesets describing the shipped surface; the first `x release`
turns them into the v0.1.0 CHANGELOG. Reseeded for the --version flag; C-free
bootstrap fixpoint holds; suites 56 / 29 / 29 on macOS, 51 / 28 (+skips) on Linux
CI, bootstrap-cfree byte-identical on both.

Part of the repository-cleanup / DX pass (with #32, #34).

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

README.md

@@ -137,7 +137,10 @@ Ludic-written PNG/DEFLATE decoder — no zlib, no external dependency.
 The compiler self-hosts to a byte-exact fixpoint and rebuilds from its IR seed
 with no C compiler; the ECS runtime, windowed + headless 2D rendering, the event
 bus, the deterministic networking stack, scenes, and save/load are all in place
-and covered by `bin/x test`.
+and covered by `bin/x test`. CI gates every push and PR on the build, the test
+suites, and that C-free fixpoint. The toolchain is versioned with SemVer
+(`ludicc --version`); releases and the `CHANGELOG.md` are cut from changesets by
+`x release`.
 
 Active work and proposals — the standard library, a fuller type system,
 rendering/animation/lighting extras, input, filesystem/IO, testing, and