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>

selfhost/main.ludic

@@ -51,6 +51,24 @@ function die(msg: pointer) -> void {
   exit(1)
 }
 
+# strip trailing newline/carriage-return/space (the VERSION file's trailing \n)
+function chomp(s: pointer) -> pointer {
+  var n = len(s)
+  while (n > 0) and ((s[n - 1] == 10) or (s[n - 1] == 13) or (s[n - 1] == 32)) { n = n - 1 }
+  return s[0..n]
+}
+
+# print "ludic <version>" and exit. The version is read at runtime from the
+# VERSION file next to LUDIC_HOME (the single source of truth a release bumps),
+# so a version change never requires reseeding the compiler.
+function show_version() -> void {
+  let home = ensure_slash(getenv_or("LUDIC_HOME", dir_of(arg(0))))
+  let v = read_file(path_join(home, "VERSION"))
+  if (v == null) { print("ludic (version unknown)") }
+  else { print(`ludic {chomp(v)}`) }
+  exit(0)
+}
+
 entry {
   var path = null
   var out  = null
@@ -66,7 +84,8 @@ entry {
   var ai = 1
   while ai < arg_count() {
     let a = arg(ai)
-    if (a == ("--windowed")) { want = 1 }
+    if (a == ("--version")) { show_version() }
+    else { if (a == ("--windowed")) { want = 1 }
     else { if (a == ("--headless")) { want = 2 }
     else { if (a == ("--emit-llvm")) { emit_ir = true }
     else { if (a == ("--fmt")) { fmt = true }
@@ -80,7 +99,7 @@ entry {
         let m = `ludicc: ignoring unknown flag {a}\n`
         file_write(file_stderr(), m, len(m))
       } else { path = a }
-    } } } } } } }
+    } } } } } } } }
     ai = ai + 1
   }