fix(compiler): add call.Vars support in scoped mode

When calling a task with vars (e.g., `task: name` with `vars:`),
those vars were not being applied in scoped mode. This fix adds
call.Vars to the variable resolution chain.

Variable priority (lowest to highest):
1. Root Taskfile vars
2. Include Taskfile vars
3. Include passthrough vars
4. Task vars
5. Call vars (NEW)
6. CLI vars

testdata/scoped_taskfiles/Taskfile.yml

@@ -42,3 +42,16 @@ tasks:
       LOL: prout_from_root
     cmds:
       - echo "{{.LOL}}"
+
+  call-with-vars:
+    desc: Test calling a task with vars override
+    cmds:
+      - task: print-name
+        vars:
+          NAME: from_caller
+
+  print-name:
+    vars:
+      NAME: default_name
+    cmds:
+      - echo "NAME={{.NAME}}"

testdata/scoped_taskfiles/testdata/TestScopedTaskfiles-scoped-call-vars.golden

@@ -0,0 +1 @@
+NAME=from_caller