fix(odds): don't return the cached no-odds marker as odds (#662)

A game ESPN had no odds for is cached as {"no_odds": True}, so it isn't
re-requested on every update. On the next update get_odds() returned that
marker from the cache as if it were odds: a truthy dict that callers took
to mean the game had some. It's still a cache hit (its ttl decides when to
ask again), but get_odds() now returns None for it -- on the cache hit and
in the stale-cache fallback after a failed fetch -- as the plugins' bundled
copies already did.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -19,6 +19,7 @@ accepts both, but the store flags the old spelling as deprecated
 
 ## Unreleased
 
+- `BaseOddsManager.get_odds()` no longer returns the cached "no odds" marker (`{"no_odds": True}`) as if it were odds. A game ESPN had no odds for is cached that way so it isn't re-requested every update; on the next update the cache hit handed the marker back, and callers saw a truthy dict. It now returns `None` for it, on the cache hit and in the stale-cache fallback after a failed fetch, as the plugins' bundled copies already did.
 - `web_interface/blueprints/api_v3/plugins.py` (3,285 lines) is split by area into `plugins.py` (installed list, enable/disable, plugin actions), `plugin_store.py`, `plugin_config.py`, `plugin_assets.py`, `plugin_health.py`, `plugin_operations.py` and `plugin_calendar.py`. Pure move: every function body and route decorator is byte-identical, and URLs and endpoint names are unchanged.
 
 - Background data fetches retry at one level instead of two. The session adapter retried a connection error three times inside every attempt of the service's own retry loop, so a dead network cost up to 16 connection attempts per request and held one of the few worker threads throughout; now it is the loop's `max_retries + 1` attempts. ESPN date-range chunks, which don't go through that loop and skip a chunk that fails, keep a small connection retry of their own so a brief blip doesn't drop a month from a cached season.