compliance: flag-gate AI portfolio + cloud sync + Stripe; de-risk prompts; harden reviewer

Implements docs/read-markets-compliance-changes.md as flag-gated changes
(no deletions) so paused features stay in the tree for future re-enable.
All four flags default False so a fresh deploy is compliance-safe.

- New env flags: PORTFOLIO_AI_ENABLED, PORTFOLIO_SYNC_ENABLED,
  TICKER_UNIVERSE_AGGREGATE_ENABLED, SUBSCRIPTIONS_ENABLED.
- Gates: /api/analyze, /api/portfolio/sync*, /api/stripe/*, /pricing,
  ticker_universe writes, portfolio_analysis.analyse(). is_paid_active()
  returns True for any auth'd user when subscriptions are paused.
- Prompts (PROMPT_VERSION 10): universal _COMPLIANCE_RIDER prepended to
  every system prompt; watch list removed; price-target / close-above-below
  / trigger / forward-state-as-description rules added; SPECULATIVE
  pivoted to regime-only scenarios; daily + weekly digests tightened.
- Reviewer: deterministic regex/lexicon pre-check fail-closed under the
  Haiku call; portfolio rider gated by PORTFOLIO_AI_ENABLED; base prompt
  sharpened for forward-state and MAR forward-opinion patterns;
  ReviewerVerdict audit table; generate_with_review retry helper.
- Migration 0026: purge portfolio_sync + ticker_universe; create
  reviewer_verdicts.
- Copy: MAR cite fixed to Art 3(1)(35) + Art 20 + Del Reg 2016/958;
  portfolio reframed as browser-only viewer in disclaimer / privacy /
  terms / about / pricing / landing (en + it). TODO(legal) marker for
  lawyer sign-off on disclaimer.
- Tests: 13 lexicon + 6 reviewer compliance regressions; conftest enables
  all flags so existing 402 tests still cover their code paths.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/routers/stripe_billing.py

@@ -34,10 +34,16 @@ from app.config import get_settings
 from app.db import get_session, utcnow
 from app.logging import get_logger
 from app.models import StripeEvent, User
+from app.services.feature_flags import require_flag
 
 
 log = get_logger("stripe_billing")
-router = APIRouter()
+# Whole router gated by SUBSCRIPTIONS_ENABLED: checkout, portal, and webhook
+# all 404 when the subscription system is paused. The webhook gate keeps us
+# from accidentally processing a late delivery while the surface is "off".
+router = APIRouter(
+    dependencies=[Depends(require_flag("SUBSCRIPTIONS_ENABLED"))],
+)
 
 
 # Cap stored payload at 16 KiB so a hostile (or buggy) sender can't