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/providers/mssql/queries/entityaddress.js

@@ -0,0 +1,105 @@
+export const ADDRESS_COLUMNS = `
+    id,
+    entity_id AS entityId,
+    first_name AS firstName,
+    name,
+    street,
+    streetnumber AS streetNumber,
+    zip,
+    city,
+    county,
+    addresstype AS addressType,
+    sort
+`;
+
+export const LIST_BY_ENTITY = `
+SELECT
+${ADDRESS_COLUMNS}
+FROM entityaddress
+WHERE entity_id = @entityId
+ORDER BY sort ASC, id ASC
+`;
+
+export const GET_BY_ENTITY_AND_ID = `
+SELECT
+${ADDRESS_COLUMNS}
+FROM entityaddress
+WHERE id = @id AND entity_id = @entityId
+`;
+
+export const GET_NEXT_SORT = `
+SELECT ISNULL(MAX(sort), -1) + 1 AS sort
+FROM entityaddress
+WHERE entity_id = @entityId
+`;
+
+export const CREATE = `
+INSERT INTO entityaddress (
+    entity_id,
+    first_name,
+    name,
+    street,
+    streetnumber,
+    zip,
+    city,
+    county,
+    addresstype,
+    sort
+)
+OUTPUT
+    INSERTED.id,
+    INSERTED.entity_id AS entityId,
+    INSERTED.first_name AS firstName,
+    INSERTED.name,
+    INSERTED.street,
+    INSERTED.streetnumber AS streetNumber,
+    INSERTED.zip,
+    INSERTED.city,
+    INSERTED.county,
+    INSERTED.addresstype AS addressType,
+    INSERTED.sort
+VALUES (
+    @entityId,
+    @firstName,
+    @name,
+    @street,
+    @streetNumber,
+    @zip,
+    @city,
+    @county,
+    @addressType,
+    @sort
+)
+`;
+
+export const UPDATE = `
+UPDATE entityaddress
+SET
+    first_name = @firstName,
+    name = @name,
+    street = @street,
+    streetnumber = @streetNumber,
+    zip = @zip,
+    city = @city,
+    county = @county,
+    addresstype = @addressType,
+    sort = @sort
+OUTPUT
+    INSERTED.id,
+    INSERTED.entity_id AS entityId,
+    INSERTED.first_name AS firstName,
+    INSERTED.name,
+    INSERTED.street,
+    INSERTED.streetnumber AS streetNumber,
+    INSERTED.zip,
+    INSERTED.city,
+    INSERTED.county,
+    INSERTED.addresstype AS addressType,
+    INSERTED.sort
+WHERE id = @id AND entity_id = @entityId
+`;
+
+export const DELETE_BY_ENTITY_AND_ID = `
+DELETE FROM entityaddress
+WHERE id = @id AND entity_id = @entityId
+`;