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/articlesupplier/create.js

@@ -3,8 +3,8 @@ import {
   CREATE as CREATE_ARTICLE_SUPPLIER,
   GET_BY_ID_AND_ARTICLE_ID,
   GET_NEXT_SORT,
-} from '../../sql/articlesupplier.js';
-import { CREATE as CREATE_PRICE } from '../../sql/price.js';
+} from '../../providers/mssql/queries/articlesupplier.js';
+import { CREATE as CREATE_PRICE } from '../../providers/mssql/queries/price.js';
 import request from '../request.js';
 import resolveArticleBySku from '../article/resolveArticleBySku.js';
 import ensureLieferantenGroup from '../supplier/ensureLieferantenGroup.js';

src/store/articlesupplier/delete.js

@@ -2,7 +2,7 @@ import {
   DELETE_BY_ID_AND_ARTICLE_ID,
   DELETE_PRICE,
   GET_BY_ID_AND_ARTICLE_ID,
-} from '../../sql/articlesupplier.js';
+} from '../../providers/mssql/queries/articlesupplier.js';
 import request from '../request.js';
 import resolveArticleBySku from '../article/resolveArticleBySku.js';
 

src/store/articlesupplier/helpers.js

@@ -1,5 +1,5 @@
-import { GET_SUPPLIER_BY_ID, SUPPLIER_GROUP_NAME } from '../../sql/entity.js';
-import { GET_COMPANY_DEFAULT_TAX } from '../../sql/articlesupplier.js';
+import { GET_SUPPLIER_BY_ID, SUPPLIER_GROUP_NAME } from '../../providers/mssql/queries/entity.js';
+import { GET_COMPANY_DEFAULT_TAX } from '../../providers/mssql/queries/articlesupplier.js';
 import request from '../request.js';
 
 export function optionalString(value) {

src/store/articlesupplier/listByArticleSku.js

@@ -1,4 +1,4 @@
-import { LIST_BY_ARTICLE_ID } from '../../sql/articlesupplier.js';
+import { LIST_BY_ARTICLE_ID } from '../../providers/mssql/queries/articlesupplier.js';
 import resolveArticleBySku from '../article/resolveArticleBySku.js';
 import { shapeArticleSupplier } from './helpers.js';
 

src/store/articlesupplier/listByEntityAndSkus.js

@@ -1,4 +1,4 @@
-import { LIST_BY_ENTITY_AND_SKUS } from '../../sql/articlesupplier.js';
+import { LIST_BY_ENTITY_AND_SKUS } from '../../providers/mssql/queries/articlesupplier.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import { assertSupplier } from './helpers.js';
 

src/store/articlesupplier/order.js

@@ -2,7 +2,7 @@ import {
   LIST_IDS_BY_ARTICLE,
   SET_TEMP_SORTS,
   UPDATE_SORT,
-} from '../../sql/articlesupplier.js';
+} from '../../providers/mssql/queries/articlesupplier.js';
 import request from '../request.js';
 import resolveArticleBySku from '../article/resolveArticleBySku.js';
 

src/store/articlesupplier/update.js

@@ -3,8 +3,8 @@ import {
   GET_BY_ID_AND_ARTICLE_ID,
   UPDATE as UPDATE_ARTICLE_SUPPLIER,
   UPDATE_PRICE,
-} from '../../sql/articlesupplier.js';
-import { CREATE as CREATE_PRICE } from '../../sql/price.js';
+} from '../../providers/mssql/queries/articlesupplier.js';
+import { CREATE as CREATE_PRICE } from '../../providers/mssql/queries/price.js';
 import request from '../request.js';
 import resolveArticleBySku from '../article/resolveArticleBySku.js';
 import ensureLieferantenGroup from '../supplier/ensureLieferantenGroup.js';