phase8: merge worker C's 0x80019B6C

0x80019B6C is the one-byte commutative-operand row that workers A and B both left
open; worker C closed it by counting the loop down from 272 with `i >= 0` and
using a byte offset into a char array, rather than the scaling form.

Registry: 153 regions. make check green at 203 tests, regions=153
disagreements=0, c_regions=153.

Worker C also removed its own unmatched g0013 draft from src/ citing the
"unmatched code stays fallback" convention, preserving it in the ignored staging
path with its evidence. Nothing referenced it.

config/regions.tsv

@@ -27,6 +27,7 @@
 0x80017C60	0x80017C6C	src/func_80017C60.c
 0x80017D1C	0x80017D48	src/func_80017D1C.c
 0x80017DD0	0x80017DF0	src/func_80017DD0.c
+0x80019B6C	0x80019B94	src/func_80019B6C.c
 0x80019C04	0x80019C10	src/func_80019C04.c
 0x8001AA9C	0x8001AAA8	src/func_8001AA9C.c
 0x8001AE3C	0x8001AE50	src/func_8001AE3C.c

src/func_80019B6C.c

@@ -0,0 +1,34 @@
+/* func_80019B6C - 0x80019B6C..0x80019B94 (40 bytes).
+ *
+ * Original words:
+ *   0x24020110  li    v0,272          i = 272
+ *   0x3C018012  lui   at,0x8012     \  address of D_80125E3C + i: the symbol's
+ *   0x00220821  addu  at,at,v0      |  high half in `at`, the byte index added,
+ *   0xAC205E3C  sw    zero,24124(at)/  the low half as the store offset
+ *   0x2442FFBC  addiu v0,v0,-68       i -= 68
+ *   0x0441FFFB  bgez  v0,-5           loop while i >= 0
+ *   0x00000000  nop
+ *   0xAF800144  sw    zero,324(gp)    D_80121A7C = 0
+ *   0x03E00008  jr    ra
+ *   0x00000000  nop
+ *
+ * Pure C, no asm. Two details are load-bearing:
+ *   - the index counts DOWN from 272 with `i >= 0`, which is the direction the
+ *     original runs (an upward `for (i = 0; i <= 272; i += 68)` gives the
+ *     `sltu`-guarded form and 8 differing words);
+ *   - the index is a BYTE offset into a `char` array. The store is a single
+ *     `sw`, so the target is a 4-byte int, but no scaling instruction appears,
+ *     which is why the symbol is declared `char D_80125E3C[]` and the store
+ *     casts to `int *`.
+ */
+extern char D_80125E3C[];
+extern int D_80121A7C;
+
+void func_80019B6C(void)
+{
+    int i;
+
+    for (i = 272; i >= 0; i -= 68)
+        *(int *)(D_80125E3C + i) = 0;
+    D_80121A7C = 0;
+}