feat(meet-kevin): prompt v2 — forward-looking action + expected_move field

User reported that the old prompt could emit 'sell' on backward-looking
capitulation ('Kevin sold after a 20% drop') — exactly the false signal
to avoid. v2 reframes every per-ticker field as forward-looking and
adds an explicit expected_move enum for the trading bot to weight.

Changes:
- New ExpectedMove enum (up_strong/up_mild/sideways/down_mild/
  down_strong/unknown) in shared/schemas + shared/models, with
  matching kevin_expected_move Postgres enum + column on
  kevin_stock_mentions (migration e5f6a7b8c9d0). NOT NULL with
  server_default 'unknown' so existing rows backfill cleanly.
- SYSTEM_PROMPT rewritten: action semantics now require a FORWARD
  view; reactive sells get downgraded to 'watch' or skipped; the
  rationale_quote must contain forward reasoning. Quality
  checklist updated.
- _ANALYSIS_TOOL JSON schema gains expected_move (required).
- prompt_version v1 → v2 in config + infra + ad-hoc CLI default.
- pipeline.py persists ticker.expected_move into the new column.

Migration safety: the column is NOT NULL DEFAULT 'unknown' so 96
existing mentions auto-fill with 'unknown' (no forward call known
for backward analyses) without breaking any reads.

Cost to backfill the 27 existing analyses with v2 prompt: ~$3 LLM
spend. A follow-up reanalyze script will replay them after this
ships.

services/meet_kevin_watcher/pipeline.py

@@ -247,6 +247,7 @@ async def process_one_video(
                 time_horizon=ticker.time_horizon.value,
                 rationale_quote=ticker.rationale_quote,
                 video_timestamp_seconds=ticker.video_timestamp_seconds,
+                expected_move=ticker.expected_move.value,
             )
             session.add(mention)