feat(web): self-onboarding multi-tenant + auth sesiune (PRD 3.3a)

Canalul web trece de la 100% deschis (hardcodat cont 1) la autentificat si
multi-tenant. Un service nou se inregistreaza din browser, primeste o cheie API
(o singura data) si o sesiune; contul se creeaza "in asteptare" (active=0) si nu
trimite la RAR pana la activarea de catre admin (tools/account.py activate).

- users + app/users.py: parole scrypt (salt per-user, eticheta parametri onorata
  la verify pentru migrare cost), email unic case-insensitive
- sesiune: SessionMiddleware (same_site=strict, https_only config) + app/web/session.py
  (current_account/web_account/require_login->LoginRequired, set_session clear-inainte)
- CSRF (app/web/csrf.py) enforce in prod inclusiv pe login/signup + rate-limit
  in-proces (app/web/ratelimit.py) pe signup si login
- signup/login/logout (app/web/auth_routes.py): signup tranzactie atomica,
  cheie-o-data, log SIGNUP pentru descoperire admin
- dashboard + import scoped pe contul sesiunii (regula NULL->cont 1); toate rutele
  web care ating date sensibile sub require_login; nomenclator ramane global
- banner "cont in asteptare" pentru conturi active=0
- gate worker: claim_one LEFT JOIN accounts COALESCE(active,1)=1 (account_id NULL=activ)

VERIFY context curat (2 runde): leak cross-account /_fragments/mapari prins+reparat.
/code-review high: csrf_token lipsa pe re-randari de eroare, scrypt_params ignorat,
login fara rate-limit -- toate reparate. 361 teste pass (de la 313).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/web/templates/_mapcoloane.html

@@ -20,6 +20,7 @@
     <form hx-post="/_import/{{ import_id }}/mapare-coloane"
           hx-target="#import-section"
           hx-swap="outerHTML">
+      <input type="hidden" name="csrf_token" value="{{ csrf_token or '' }}">
 
       <div style="margin-bottom:8px; display:flex; align-items:center; gap:10px; flex-wrap:wrap;">
         <label for="format-data" style="font-size:13px; color:var(--muted);">