test(asm): lock indirect-memory =*m rejection (Phase G prep)

Adds examples/1652-platform-asm-indirect-mem.sx exercising a `=*m -> @x`
indirect-memory place output. Currently rejected loudly at lowering
("not yet implemented"); this locks that behavior as a passing test.
The next commit implements indirect-memory outputs and flips this
example to run end-to-end (store-through-pointer → 42).

examples/1652-platform-asm-indirect-mem.sx

@@ -0,0 +1,19 @@
+// ASM stream — indirect-memory (`=*m`) place output. The place address is passed
+// to the asm as a pointer and the asm writes THROUGH it (no return slot): here
+// `str x9, %[out]` stores 42 into `x`'s storage directly. Distinct from a
+// write-through `=` output (which returns a value that is then stored). Mixes a
+// value output and an input below to exercise operand ordering. aarch64-pinned;
+// ir-only elsewhere (the `.ir` locks the `=*m` constraint + `elementtype` attr).
+poke :: () -> i64 {
+    x : i64 = 0;
+    asm volatile {
+        #string ASM
+        mov x9, #42
+        str x9, %[out]
+ASM,
+        [out] "=*m" -> @x,
+        clobbers(.x9),
+    };
+    return x;   // 42 — written through the pointer
+}
+main :: () -> i64 { return poke(); }

examples/expected/1652-platform-asm-indirect-mem.exit

@@ -0,0 +1 @@
+1

examples/expected/1652-platform-asm-indirect-mem.stderr

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+error: indirect-memory (`*`) asm outputs are not yet implemented
+  --> examples/1652-platform-asm-indirect-mem.sx:9:5
+   |
+ 9 |     asm volatile {
+   |     ^^^^^^^^^^^^^^
+10 |         #string ASM
+   | ^^^^^^^^^^^^^^^^^^^
+11 |         mov x9, #42
+   | ^^^^^^^^^^^^^^^^^^^
+12 |         str x9, %[out]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+13 | ASM,
+   | ^^^^
+14 |         [out] "=*m" -> @x,
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+15 |         clobbers(.x9),
+   | ^^^^^^^^^^^^^^^^^^^^^^
+16 |     };
+   | ^^^^^

examples/expected/1652-platform-asm-indirect-mem.stdout

@@ -0,0 +1 @@
+