fix(interpreter): initialize assoc/indexed arrays for local -A/-a (#886)

## Summary
- `local -A m` followed by `m["a"]="1"` produced an indexed array
instead of associative, because `execute_local_builtin` only inserted
into `call_stack.locals` without creating the `assoc_arrays` entry
- Initialize the appropriate array type when `local -A` or `-a` is used
without a compound assignment value
- Fix applies to both function-scope and global-scope paths
- Add spec tests `assoc_local_declare_then_assign` and
`assoc_local_keys_in_cmdsub`

## Test plan
- [x] New spec tests pass
- [x] All 1812 bash spec tests pass (100%)
- [x] Full `cargo test --all-features` passes
- [x] `cargo fmt --check` and `cargo clippy` clean

Closes #875

Author: chaliy

crates/bashkit/src/interpreter/mod.rs

@@ -4353,6 +4353,11 @@ impl Interpreter {
                         .unwrap()
                         .locals
                         .insert(arg.to_string(), String::new());
+                    if flags.assoc {
+                        self.assoc_arrays.entry(arg.to_string()).or_default();
+                    } else if flags.array {
+                        self.arrays.entry(arg.to_string()).or_default();
+                    }
                     if flags.integer {
                         self.variables
                             .insert(format!("_INTEGER_{}", arg), "1".to_string());
@@ -4437,7 +4442,13 @@ impl Interpreter {
                             .insert(var_name.to_string(), value.to_string());
                     }
                 } else if !is_internal_variable(arg) {
-                    self.insert_variable_checked(arg.to_string(), String::new());
+                    if flags.assoc {
+                        self.assoc_arrays.entry(arg.to_string()).or_default();
+                    } else if flags.array {
+                        self.arrays.entry(arg.to_string()).or_default();
+                    } else {
+                        self.insert_variable_checked(arg.to_string(), String::new());
+                    }
                 }
             }
         }

crates/bashkit/tests/spec_cases/bash/assoc-arrays.test.sh

@@ -173,6 +173,35 @@ b=2
 c=3
 ### end
 
+### assoc_local_declare_then_assign
+myfunc() {
+  local -A m
+  m["a"]="1"
+  m["b"]="2"
+  echo "count: ${#m[@]}"
+  for k in "${!m[@]}"; do echo "key=$k"; done | sort
+}
+myfunc
+### expect
+count: 2
+key=a
+key=b
+### end
+
+### assoc_local_keys_in_cmdsub
+myfunc() {
+  local -A m
+  m["a"]="1"
+  m["b"]="2"
+  result="$(printf '%s\n' "${!m[@]}" | sort)"
+  echo "result: [$result]"
+}
+myfunc
+### expect
+result: [a
+b]
+### end
+
 ### assoc_iteration
 declare -A m
 m[a]="1"