feat(release): add CalVer plugin for YYYY.M.D[-N] versioning

Adds a local semantic-release plugin (release/calver.cjs) that overrides
nextRelease.version in the prepare lifecycle with a calendar-based version.
Checks existing git tags for today to append an iteration suffix when
multiple releases happen on the same day (e.g. 2026.3.17-1, 2026.3.17-2).

Uses UTC date for timezone-consistent CI behavior. Plugin runs before
@semantic-release/npm and @semantic-release/git so all downstream plugins
use the CalVer version string. Commit-analyzer still gates whether a
release fires (fix:/feat:/perf:/BREAKING CHANGE only).

Author: blazejpawlak

.releaserc.json

@@ -4,6 +4,7 @@
   "plugins": [
     "@semantic-release/commit-analyzer",
     "@semantic-release/release-notes-generator",
+    "./release/calver.cjs",
     [
       "@semantic-release/changelog",
       {

release/calver.cjs

@@ -0,0 +1,38 @@
+"use strict";
+// CalVer semantic-release plugin — YYYY.M.D[-iteration]
+// Overrides nextRelease.version in the prepare lifecycle before
+// @semantic-release/npm and @semantic-release/git consume it.
+const { execSync } = require("child_process");
+
+module.exports = {
+  prepare(pluginConfig, context) {
+    const { nextRelease, logger } = context;
+
+    const now = new Date();
+    const base = `${now.getUTCFullYear()}.${now.getUTCMonth() + 1}.${now.getUTCDate()}`;
+
+    // Find any tags already published today
+    let existing = [];
+    try {
+      const out = execSync(`git tag -l "${base}" "${base}-*"`, { encoding: "utf8" });
+      existing = out.trim().split("\n").filter(Boolean);
+    } catch {
+      existing = [];
+    }
+
+    let version;
+    if (existing.length === 0) {
+      version = base;
+    } else {
+      const iters = existing.map((t) => {
+        const m = t.match(/-(\d+)$/);
+        return m ? parseInt(m[1], 10) : 0;
+      });
+      version = `${base}-${Math.max(...iters) + 1}`;
+    }
+
+    logger.log("CalVer: %s → %s", nextRelease.version, version);
+    nextRelease.version = version;
+    nextRelease.gitTag = `v${version}`;
+  },
+};