Second hardening pass: atomic data writes, bible-passage limits, webhook SSRF guard, note sanitizing, CI gates; v2.10.1

- Atomic temp-file + rename for all JSON data writes (no truncated files on crash)
- /api/bible-passage: rate limit, range caps (60 verses), bounded cache
- Admin webhooks: https-only, block private/internal/Tailscale addresses (checked at registration and delivery), no redirects
- Resend webhook token compare is timing-safe
- DOMPurify on rendered study notes and broadcast preview
- CI runs lint + tests before build
- Permissions-Policy and HSTS (production) headers; JSON error handler for /api
- Tests for URL safety and atomic writes

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

test/atomic-write.test.js

@@ -0,0 +1,26 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { mkdtemp, readFile, readdir, writeFile as plainWrite, rm } from 'node:fs/promises'
+import os from 'node:os'
+import path from 'node:path'
+import { writeFile } from '../server/atomic-write.js'
+
+test('replaces file contents and leaves no temp files', async () => {
+  const dir = await mkdtemp(path.join(os.tmpdir(), 'atomic-'))
+  const file = path.join(dir, 'a.json')
+  await plainWrite(file, 'old')
+  await writeFile(file, '{"ok":true}', 'utf8')
+  assert.equal(await readFile(file, 'utf8'), '{"ok":true}')
+  assert.deepEqual(await readdir(dir), ['a.json'])
+  await rm(dir, { recursive: true })
+})
+
+test('a failed write keeps the old file and cleans up', async () => {
+  const dir = await mkdtemp(path.join(os.tmpdir(), 'atomic-'))
+  const file = path.join(dir, 'a.json')
+  await plainWrite(file, 'old')
+  await assert.rejects(() => writeFile(file, { not: 'a string' }))
+  assert.equal(await readFile(file, 'utf8'), 'old')
+  assert.deepEqual(await readdir(dir), ['a.json'])
+  await rm(dir, { recursive: true })
+})