fix(db) loadSubset when orderby has multiple columns (#926)

* fix(db) loadSubset when orderby has multiple columns

failing test for multiple orderby and loadsubset

push down multiple orderby predicates to load subset

split order by cursor predicate build into two, inprecise wider band for local lading, precise for the sync loadSubset

new e2e tests for composite orderby and pagination

changeset

when doing gt/lt comparisons to a bool cast to string

fix: use non-boolean columns in multi-column orderBy e2e tests

Electric/PostgreSQL doesn't support comparison operators (<, >, <=, >=)
on boolean types. Changed tests to use age (number) and name (string)
columns instead of isActive (boolean) to avoid this limitation.

The core multi-column orderBy functionality still works correctly -
this is just a test adjustment to work within Electric's SQL parser
constraints.

* ci: apply automated fixes

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

Author: samwillis

.changeset/multi-column-orderby-loadsubset.md

@@ -0,0 +1,18 @@
+---
+'@tanstack/db': patch
+---
+
+Enhanced multi-column orderBy support with lazy loading and composite cursor optimization.
+
+**Changes:**
+
+- Create index on first orderBy column even for multi-column orderBy queries, enabling lazy loading with first-column ordering
+- Pass multi-column orderBy to loadSubset with precise composite cursors (e.g., `or(gt(col1, v1), and(eq(col1, v1), gt(col2, v2)))`) for backend optimization
+- Use wide bounds (first column only) for local index operations to ensure no rows are missed
+- Use precise composite cursor for sync layer loadSubset to minimize data transfer
+
+**Benefits:**
+
+- Multi-column orderBy queries with limit now support lazy loading (previously disabled)
+- Sync implementations (like Electric) can optimize queries using composite indexes on the backend
+- Local collection uses first-column index efficiently while backend gets precise cursor