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>

changes/README.md

@@ -0,0 +1,25 @@
+# Changesets
+
+A **changeset** is one small Markdown file describing a single user-facing change,
+dropped in this directory. `x release` consumes every changeset here into a new
+`CHANGELOG.md` section, bumps `VERSION`, and deletes the consumed files.
+
+## Format
+
+```
+bump: minor
+type: feat
+One or more lines describing the change, in the past-agnostic imperative used in
+the changelog. Markdown is fine.
+```
+
+- `bump:` — `major`, `minor`, or `patch` (SemVer). The release version is bumped
+  by the **highest** level among the pending changesets (unless `x release <level>`
+  overrides it).
+- `type:` — the Conventional Commit type (`feat`, `fix`, `perf`, `docs`, …); it
+  becomes the bold prefix of the changelog bullet.
+
+## Adding one
+
+Create a file with a short, unique name, e.g. `changes/regex-namespace.md`. Any
+filename works except this `README.md`, which the release step always skips.