feat(store): fetch contributions incrementally and persist history in SQLite

Bound each provider's startFetch()/resolveFetch() to an optional
since/until window, wire a SQLite-backed ContributionStore into
ContributionAggregator (fetch only the trailing window past the last
stored date, merge into the store, prune by CONTRIBUTIONS_RETENTION_DAYS),
and add a graph:contributions:refetch command to force a full or ranged
re-fetch in <=365-day chunks. This is the root fix for the full
365-day-refetch timeout that used to hit on every cache miss.

tests/Unit/Service/Provider/ProbeTraitTest.php

@@ -31,7 +31,7 @@ final class ProbeTraitTest extends TestCase
             public function isConfigured(): bool { return $this->configured; }
             public function getName(): string { return 'test'; }
             public function ping(): void { ($this->ping)(); }
-            public function startFetch(): mixed { return null; }
+            public function startFetch(?\DateTimeImmutable $since = null, ?\DateTimeImmutable $until = null): mixed { return null; }
             public function resolveFetch(mixed $handle): array { return []; }
         };
     }