refactor(office): generalize DataTable layout and document TUI table skill

Unify project/user flex column layout into layoutFlexTable with per-subject
policy in model. Add office-tui-table skill and AGENTS notes; fix CI go mod
tidy drift and test matrix Go version to match go.mod 1.25.

Co-authored-by: Cursor <cursoragent@cursor.com>

cmd/office/model/table_layout_test.go

@@ -0,0 +1,18 @@
+package model
+
+import "testing"
+
+func TestTableFlexLayoutFor(t *testing.T) {
+	proj, ok := TableFlexLayoutFor(SubjectProjects)
+	if !ok || proj.FlexColumnKey != "title" || proj.MinFlexWidth != 12 {
+		t.Fatalf("projects layout=%+v ok=%v", proj, ok)
+	}
+	users, ok := TableFlexLayoutFor(SubjectUsers)
+	if !ok || users.FlexColumnKey != "email" {
+		t.Fatalf("users layout=%+v", users)
+	}
+	_, ok = TableFlexLayoutFor(SubjectTasks)
+	if ok {
+		t.Fatal("tasks should use scrolling layout")
+	}
+}