refactor: introduce database provider abstraction, isolate MSSQL layer

- Add provider contract (src/providers/provider.js): query() -> {rows,
  rowsAffected, insertId}, callback transaction(fn), exec() for stored
  procs, initialize/purge lifecycle
- Add MssqlProvider (src/providers/mssql/index.js) wrapping an mssql
  ConnectionPool with normalized results, tx commit/rollback and
  constraint-error classifiers (unique 2627/2601, FK 547)
- LibDashStore constructor now takes a provider instead of a pool
  (breaking); adds LibDashStore.create() async factory; keeps pool as
  transitional bridge until store modules are converted (see TODO.md)
- Move MSSQL-specific code into the provider: src/sql/* ->
  src/providers/mssql/queries/*, src/schema.js ->
  src/providers/mssql/schema.js, purge SQL -> purgeSql.js
- Update scripts, generate-schema-graph.js and package.json exports
  (./providers/mssql, ./providers/provider)
- Add TODO.md with the remaining provider/SQLite migration plan

No SQL or behavioral changes.

src/store/manifestattachment/add.js

@@ -5,7 +5,7 @@ import {
   CREATE_FILE,
   CREATE_ATTACHMENT,
   GET_NEXT_SORT,
-} from '../../sql/manifestattachment.js';
+} from '../../providers/mssql/queries/manifestattachment.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import resolveManifestAccess from './resolveManifestAccess.js';
 import request from '../request.js';

src/store/manifestattachment/getById.js

@@ -1,4 +1,4 @@
-import { GET_BY_ID } from '../../sql/manifestattachment.js';
+import { GET_BY_ID } from '../../providers/mssql/queries/manifestattachment.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import resolveManifestAccess from './resolveManifestAccess.js';
 import { parseMeta } from './listByManifestId.js';

src/store/manifestattachment/listByManifestId.js

@@ -1,4 +1,4 @@
-import { LIST_BY_MANIFEST } from '../../sql/manifestattachment.js';
+import { LIST_BY_MANIFEST } from '../../providers/mssql/queries/manifestattachment.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import resolveManifestAccess from './resolveManifestAccess.js';
 import request from '../request.js';

src/store/manifestattachment/order.js

@@ -2,7 +2,7 @@ import {
   LIST_IDS_BY_MANIFEST,
   SET_TEMP_SORTS,
   UPDATE_SORT,
-} from '../../sql/manifestattachment.js';
+} from '../../providers/mssql/queries/manifestattachment.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import resolveManifestAccess from './resolveManifestAccess.js';
 import request from '../request.js';

src/store/manifestattachment/remove.js

@@ -1,4 +1,4 @@
-import { FIND_ATTACHMENT, DELETE_FILE } from '../../sql/manifestattachment.js';
+import { FIND_ATTACHMENT, DELETE_FILE } from '../../providers/mssql/queries/manifestattachment.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import resolveManifestAccess from './resolveManifestAccess.js';
 import request from '../request.js';

src/store/manifestattachment/resolveManifestAccess.js

@@ -1,4 +1,4 @@
-import { CHECK_MANIFEST_ACCESS } from '../../sql/manifestattachment.js';
+import { CHECK_MANIFEST_ACCESS } from '../../providers/mssql/queries/manifestattachment.js';
 import request from '../request.js';
 
 /** Ensure manifest belongs to company. Throws Manifest not found. */