#597 auto-bump deploy counter on every redeploy

scripts/update-version.mjs now maintains a `deployCount` integer and
rewrites `version` as `${baseVersion}.${deployCount}` every time the
build hash actually changes. When build is unchanged (re-run without
new commit) it still no-ops, matching prior behaviour, so re-running
the build twice in CI doesn't inflate the counter.

version.json shape:
  {
    "baseVersion": "0.1.0-dev",   <- stable, manually owned
    "version":     "0.1.0-dev.42", <- baseVersion + "." + deployCount
    "build":       "20260518.f942f101",
    "deployCount": 42
  }

Migration: on the very first run after this change, if `baseVersion`
is missing, the script derives it from the existing `version` field
by stripping any trailing `.<digits>`. If `deployCount` is missing it
seeds from that same trailing counter, so a repo that was already
hand-numbered (e.g. "0.1.0-dev.12") doesn't reset progress to 0.

Verified manually:
- Re-run with no new commit -> "build unchanged: ...", file untouched.
- New build -> bumps deployCount by exactly 1, rewrites version.
- Manually editing baseVersion to "0.2.0" -> next bump yields
  "0.2.0.<count+1>", manual base preserved.

api-server reads version.json statically (import with type: "json"),
so no API change is needed — the new fields flow through to
/api/system/version automatically. admin.tsx just prints
data.current.version, no regex parsing, so the new suffixed string
shows up in the System Updates card with no UI edit.

version.json reset to baseVersion=0.1.0-dev, version=0.1.0-dev,
deployCount=0 so the next legitimate Mac docker build bumps cleanly
to dev.1 on first redeploy.

scripts/update-version.mjs

@@ -22,11 +22,49 @@ try {
 
 const build = `${date}.${commit}`;
 const current = JSON.parse(readFileSync(versionPath, "utf8"));
-const next = { ...current, build };
+
+// #597: derive the stable base from the existing `version` field on
+// first run so older repos migrate cleanly. e.g. "0.1.0-dev.5" -> base
+// "0.1.0-dev", count 5. A bare "0.1.0-dev" (no trailing .N) just stays
+// the base and starts counting from the current deployCount (or 0).
+const TRAILING_COUNTER = /\.(\d+)$/;
+function deriveBase(versionStr) {
+  if (typeof versionStr !== "string" || versionStr.length === 0) {
+    return "0.1.0-dev";
+  }
+  const m = versionStr.match(TRAILING_COUNTER);
+  return m ? versionStr.slice(0, -m[0].length) : versionStr;
+}
+
+const baseVersion =
+  typeof current.baseVersion === "string" && current.baseVersion.length > 0
+    ? current.baseVersion
+    : deriveBase(current.version);
+
+let deployCount = Number.isInteger(current.deployCount)
+  ? current.deployCount
+  : (() => {
+      // Seed from the trailing counter on the existing version string
+      // so first migration doesn't reset progress to 0 if the user had
+      // already been numbering manually (e.g. "0.1.0-dev.12").
+      const m =
+        typeof current.version === "string"
+          ? current.version.match(TRAILING_COUNTER)
+          : null;
+      return m ? parseInt(m[1], 10) : 0;
+    })();
 
 if (current.build === build) {
+  // No new commit since last run -> nothing to do. Don't bump the
+  // counter and don't rewrite the file. This matches pre-#597 behaviour
+  // so re-running the build twice in CI doesn't inflate the counter.
   console.log(`[update-version] build unchanged: ${build}`);
 } else {
+  deployCount += 1;
+  const version = `${baseVersion}.${deployCount}`;
+  const next = { baseVersion, version, build, deployCount };
   writeFileSync(versionPath, JSON.stringify(next, null, 2) + "\n");
-  console.log(`[update-version] ${current.build} -> ${build}`);
+  console.log(
+    `[update-version] ${current.build} -> ${build} | ${current.version ?? "<none>"} -> ${version}`,
+  );
 }