feat(routing): wire AI target_asset end-to-end — bot trades the right perp

Closes the loop on the asset-routing prompt change. Previously the v5
prompt emitted target_asset (e.g. SOL, TRUMP) but bot_engine still
read price_impact_asset and only ever traded BTC/ETH. Now the trade
actually fires on whatever perp the AI picked.

Schema (alembic 006):
  posts.target_asset       (str)   — HL perp ticker, any of the universe
  posts.category           (str)   — 6-class enum (direct_named, etc.)
  posts.expected_move_pct  (float) — AI's 1h move estimate

Wiring:
  truth_social.py persists the three fields when creating Post rows.
  bot_engine.py routing:  asset = target_asset || price_impact_asset || BTC
  Old rows (target_asset=NULL) fall back to legacy BTC/ETH path — no
  retroactive scoring needed; new rows route correctly from now on.

Hyperliquid trader doesn't need changes — `coin` is already a parameter,
and analysis.py validated against HL_PERPS before storing target_asset
so by the time bot_engine reads the field, it's guaranteed tradeable.

Deployment:
  alembic upgrade head    # adds the 3 columns
  Restart api container

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

alembic/versions/006_add_target_asset.py

@@ -0,0 +1,34 @@
+"""Add target_asset / category / expected_move_pct to posts (v5 routing)
+
+Revision ID: 006
+Revises: 005
+Create Date: 2026-05-08 00:00:00.000000
+
+The v5 AI prompt outputs not just signal direction but also which specific
+perp to trade (could be BTC/ETH/SOL/TRUMP/anything on Hyperliquid). The
+bot reads `target_asset` to route the trade. `price_impact_asset` stays
+bound to BTC/ETH for the existing price_impact_monitor.
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "006"
+down_revision: Union[str, None] = "005"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    with op.batch_alter_table("posts") as batch_op:
+        batch_op.add_column(sa.Column("target_asset", sa.String(16), nullable=True))
+        batch_op.add_column(sa.Column("category", sa.String(24), nullable=True))
+        batch_op.add_column(sa.Column("expected_move_pct", sa.Float(), nullable=True))
+
+
+def downgrade() -> None:
+    with op.batch_alter_table("posts") as batch_op:
+        batch_op.drop_column("expected_move_pct")
+        batch_op.drop_column("category")
+        batch_op.drop_column("target_asset")