Add professional PHPDoc (summary + @param/@return) to the remaining
public methods that had none or only partial coverage: GraphController's
actions, ContributionStore's accessors, SvgRenderer's render() and
private helpers (with concrete array-shape annotations), ProbeTrait,
ProviderHealthChecker, ProviderStatus, and the Contribution entity.
Also adds the matching @return shapes on SvgRendererTest's data
providers.
- Fix add()'s upsert SQL (was invalid SQL from typos) and use it for
the new merge() as well.
- Fix remove()'s missing FROM keyword and drop the unindexed LIKE scan
in favor of an exact match.
- Add latestDate(), all() with optional sinceDays filtering, and
prune() with a retention-day cutoff.
- Add Contribution (immutable value object) and ContributionCollection
(IteratorAggregate + Countable) so all() returns something typed
instead of a raw date => count array.
- Cover all of the above with unit tests against an in-memory SQLite
database.
haylan