feat: add a Salesforce Nonprofit Cloud gift export reader (ingest preset)

[shivamlalakiya]

What's needed

philanthropy.ingest has three donor-CRM gift bridges today: CiviCRM, Blackbaud Raiser's Edge, and Salesforce NPSP. Each is a thin, CRM-specific header-alias map plus a commitment/payment exclusion filter (a pledge and the payment against it must never both count toward total_gift_amount), delegating the actual roll-up to the shared aggregator in philanthropy/ingest/_civicrm.py. This issue adds the same bridge for Salesforce Nonprofit Cloud — Salesforce's newer nonprofit data model (Gift, Payment, and related objects), distinct from the older NPSP package this repo already supports.

Where to look

File	Purpose
philanthropy/ingest/_npsp.py	Closest existing example: same underlying platform (Salesforce), header aliasing, a documented default exclusion set, delegation to the shared aggregator
philanthropy/ingest/_raisers_edge.py	A second example of the same pattern
philanthropy/ingest/_civicrm.py	The shared aggregator (civicrm_contributions_to_features, read_civicrm_contributions) and the private helpers (_REQUIRED, _canonical, _normalise_headers, _to_frame, _empty_feature_frame) both examples import and reuse
tests/test_npsp.py	The test depth expected of your new tests/test_nonprofit_cloud.py
philanthropy/cli.py	_FEATURE_SOURCES and the features --source dispatch — wire your new source in the same shape, unless the read_gifts preset registry (a separate, in-flight PR extracting the shared aggregator into a source-keyed dispatcher) has already landed by the time you start, in which case register there instead

What to build

1. philanthropy/ingest/_nonprofit_cloud.py: a header-alias map from Nonprofit Cloud's real export labels and API field names onto the canonical contact_id / receive_date / total_amount / gift_type names _civicrm.py already understands; a documented default exclusion parameter for whatever this data model's pledge/commitment-vs-payment split actually is (Nonprofit Cloud separates Gift and Payment as related objects rather than NPSP's stage-on-one-Opportunity approach — find out exactly how from the docs, don't assume it matches NPSP); a nonprofit_cloud_gifts_to_features(...) function; and a read_nonprofit_cloud_gifts(path) reader delegating to read_civicrm_contributions.
2. Verify every field name and every commitment/payment vocabulary term against Salesforce's own public Nonprofit Cloud documentation before writing it down — do not guess or recall from memory. Cite the doc URLs you actually used in your PR body, the way PR #233 does for NPSP. Start from Salesforce's own help site and Trailhead, searching for "Nonprofit Cloud" data model / Gift / Payment objects — this issue does not assert any field name as fact, confirm everything yourself.
3. Export the new names from philanthropy/ingest/__init__.py (__all__, alphabetical) and add a stability-tier row to docs/reference/index.md (Tier 2/Beta, same reasoning as the other three bridges — a test enforces every public symbol has a row).
4. tests/test_nonprofit_cloud.py at the depth of tests/test_npsp.py: header aliasing from every spelling the docs name, the commitment/payment double-count trap and its exclusion, the exclusion set being documented/overridable/disabled by None, currency parsing, schema/dtypes, empty input, missing required columns.
5. CHANGELOG.md entry under ## [Unreleased], and add yourself to CONTRIBUTORS.md if you'd like.

Hard constraints (same as the rest of this ingest series)

• Dependencies stay scikit-learn/pandas/numpy/joblib only — no new package, no API client, no network code anywhere in philanthropy/. This is a file-export reader (CSV in, DataFrame out), never a live API connector.
• No new estimator class.
• Build the exclusion logic from Salesforce's own public docs only — never from an institution's actual configuration or data.
• Follow AGENTS.md's order: implement, export, verify with python -c "from philanthropy.ingest import nonprofit_cloud_gifts_to_features, read_nonprofit_cloud_gifts; print('OK')", then write tests, then make ci.

Verifying

python -m pip install -e ".[dev]"
python -c "from philanthropy.ingest import nonprofit_cloud_gifts_to_features, read_nonprofit_cloud_gifts; print('OK')"
make ci
make riskcov

Claim this issue with a comment before starting (see CONTRIBUTING.md); a maintainer assigns within 24 hours.