fix bulk fundamentals: rate limits masked by partial FMP success

Root cause of "price plan needed in bulk but fine on manual reload": on free
tiers FMP returns only market cap (others 402) and the chain merged that as a
partial success — so when the Finnhub/Alpha Vantage fallbacks were rate-limited
during a bulk run, the chain silently returned market-cap-only and the
collector's backoff never engaged. Manual single fetches worked because the
fallbacks weren't throttled at that moment.

Fixes:
- Chain distinguishes RateLimitError from other failures: if a fallback is
  rate-limited and fields are still missing, raise RateLimitError (unless
  allow_partial=True) so the collector backs off and retries.
- Bulk job paces requests (fundamental_request_spacing_seconds, default 3s) to
  stay under Finnhub's ~60/min, and on retry-exhaustion stores partial data and
  continues instead of aborting the whole run.
- Manual fetch passes allow_partial=True so a lone 429 doesn't fail the refresh.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/config.py

@@ -49,6 +49,10 @@ class Settings(BaseSettings):
     alerts_frequency: str = "hourly"
     fundamental_rate_limit_retries: int = 3
     fundamental_rate_limit_backoff_seconds: int = 15
+    # Pause between tickers in the bulk fundamentals job. Free tiers throttle
+    # hard (Finnhub ~60 calls/min, ~3 calls/ticker → ~3s/ticker); without
+    # spacing the job bursts straight into 429s. 0 disables.
+    fundamental_request_spacing_seconds: float = 3.0
 
     # Scoring Defaults
     default_watchlist_auto_size: int = 10