Remove dead currentSnapshot, sendJson, readJsonBody helpers

REC-122:

- `currentSnapshot()` had no caller (the `cachedSnapshot` variable it
  wrapped is still legitimately read directly by
  `refreshWitnesses`'s overlap-skip branch, so only the unused wrapper
  function was removed, not the variable).
- `sendJson` and `readJsonBody` are remnants of a removed HTTP
  ingress; neither has a caller. `httpError`, which `readJsonBody`
  called internally, is kept — it is used by 13 other call sites
  throughout the file.

Kill attempts that failed: none.
- `rg -n '\bcurrentSnapshot\b' scripts/weksa-daemon.mjs` -> only its
  now-removed declaration (repeated the census command against
  current HEAD before editing).
- `rg -n '\bsendJson\b|\breadJsonBody\b' scripts/weksa-daemon.mjs` ->
  only the two now-removed definitions.
- Not exported from the file and no other file requires/imports
  scripts/weksa-daemon.mjs as a module, so no cross-repo consumer is
  possible for these unexported local functions.

Checks run: `node --check scripts/weksa-daemon.mjs` -> syntax OK. No
package.json/test suite exists in this repo to run beyond that.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/weksa-daemon.mjs

@@ -174,13 +174,6 @@ async function publishWitnesses() {
   return snapshot;
 }
 
-async function currentSnapshot() {
-  if (!cachedSnapshot) {
-    await refreshWitnesses("snapshot-demand");
-  }
-  return cachedSnapshot;
-}
-
 async function refreshWitnesses(reason) {
   if (witnessRefreshRunning) {
     await appendLog(`skipped overlapping witness refresh reason=${reason}`);
@@ -1108,32 +1101,6 @@ async function writeJson(path, value) {
   await writeFile(path, `${JSON.stringify(value, null, 2)}\n`, "utf8");
 }
 
-function sendJson(response, statusCode, value) {
-  response.writeHead(statusCode, { "content-type": "application/json; charset=utf-8" });
-  response.end(`${JSON.stringify(value, null, 2)}\n`);
-}
-
-async function readJsonBody(request) {
-  const chunks = [];
-  let byteLength = 0;
-  for await (const chunk of request) {
-    byteLength += chunk.length;
-    if (byteLength > 1_000_000) {
-      throw httpError(413, "request body is too large");
-    }
-    chunks.push(chunk);
-  }
-  const text = Buffer.concat(chunks).toString("utf8").trim();
-  if (!text) {
-    throw httpError(400, "request body is empty");
-  }
-  try {
-    return JSON.parse(text);
-  } catch (error) {
-    throw httpError(400, `invalid JSON body: ${error.message}`);
-  }
-}
-
 function httpError(statusCode, message) {
   const error = new Error(message);
   error.statusCode = statusCode;