fix: complete v5 routing — API exposure, rescore persistence, leverage cap, key backup doc

Three plumbing fixes + one ops doc that close the gaps from the audit.

scripts/rescore_v5.py
  Was overwriting only signal/conf/reasoning/sentiment/relevant/
  prefilter_reason/analysis_version. Now also persists target_asset,
  category, expected_move_pct — without these the bot can't route
  rescored posts correctly (would silently fall back to BTC).

app/schemas.py + app/api/posts.py
  TrumpPost response model didn't expose target_asset/category/
  expected_move_pct, so the frontend had no way to display "this
  signal will trade SOL". Added the three fields + mapping in
  _post_to_schema(). Pre-v5 posts return null. No frontend changes
  yet — display work is a follow-up.

app/services/hyperliquid.py
  HL caps max leverage per asset (BTC/ETH 50×, SOL 20×, memes 3-5×).
  set_leverage() always tried to push self._leverage — if user set
  30× and bot routed to TRUMP, HL rejected the order and the trade
  silently dropped. Added _get_max_leverage() (queries meta()'s
  maxLeverage field) and _clip_leverage() that caps to HL's max.
  set_leverage now returns the effective leverage so callers can
  use it for notional sizing if needed.

deploy/ENCRYPTION_KEY_BACKUP.md
  Documented mandatory backup procedure for the symmetric key that
  encrypts every user's HL API key. Lost key = all users' bots dead
  with no recovery. Includes rotation procedure + quarterly test
  step + things-not-to-do list.

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

app/api/posts.py

@@ -57,6 +57,10 @@ def _post_to_schema(post: Post) -> TrumpPost:
         analysis_version=post.analysis_version,
         relevant=post.relevant,
         price_impact=price_impact,
+        # v5 routing fields — null for pre-v5 posts
+        target_asset=post.target_asset,
+        category=post.category,
+        expected_move_pct=post.expected_move_pct,
     )