Security & hardening pass: scrypt password hashing, persisted admin sessions, upvote/analytics rate limits, dependency fixes, healthcheck, lint cleanup; v2.10.0

- Study passwords: salted scrypt; legacy SHA-256 hashes verified and upgraded on login
- Admin sessions persisted (hashed tokens) so deploys no longer log the admin out
- Upvotes: rate limit + one per client per question, approved questions only; rate limit on analytics play/event
- npm audit: 46 -> 4 vulnerabilities (tiptap bumped to 3.31.4)
- Untrack per-user data (study users/notes/progress/etc.) from git
- Dockerfile HEALTHCHECK; node --test suite for password hashing
- Fix email template cards remounting (lost input focus) on each keystroke
- Lint: 34 errors -> 0

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

src/components/ContactForm.tsx

@@ -2,7 +2,7 @@ import { useState, useEffect } from 'react'
 import type { ChangeEvent } from 'react'
 import { useNavigate, useSearchParams } from 'react-router-dom'
 
-const EMAIL_REGEX = /^[a-zA-Z0-9._%+\-]{1,64}@[a-zA-Z0-9.\-]{1,253}\.[a-zA-Z]{2,}$/
+const EMAIL_REGEX = /^[a-zA-Z0-9._%+-]{1,64}@[a-zA-Z0-9.-]{1,253}\.[a-zA-Z]{2,}$/
 
 interface ContactFields {
   firstName: string

src/components/NuggetsHostPortal.tsx

@@ -18,7 +18,7 @@ function formatBytes(b: number) {
 }
 
 function saveDraft(ep: string, passage: string, desc: string) {
-  try { localStorage.setItem(DRAFT_KEY, JSON.stringify({ ep, passage, desc })) } catch {}
+  try { localStorage.setItem(DRAFT_KEY, JSON.stringify({ ep, passage, desc })) } catch { /* storage unavailable */ }
 }
 
 function loadDraft() {
@@ -30,7 +30,7 @@ function loadDraft() {
 }
 
 function clearDraft() {
-  try { localStorage.removeItem(DRAFT_KEY) } catch {}
+  try { localStorage.removeItem(DRAFT_KEY) } catch { /* storage unavailable */ }
 }
 
 export function NuggetsHostPortal() {