fix: define every capability word, including the ones that read zero (#2)

⚠️ 在把一个「查询能力」的可移植程序移到这个后端时实测:

    ld.lld: error: undefined symbol: kal_fs_props
    >>> referenced by fs.cppm:136
    >>>               obj/main.o:(kal::fs::properties@openkal.fs())

    ld.lld: error: undefined symbol: kal_task_props

那个程序**一次文件系统调用都没有**。引用来自「询问」本身 ——
规范的查询是这些对象上的 inline 函数:

    inline props properties() { return props{kal_fs_props}; }

所以一个只是**问**「这台机器有没有文件系统」的程序,就会取 `kal_fs_props`
的地址。在一台没有文件系统的机器上不定义它,等于让这个问题以最强的方式
无法回答:它链接不过去。

⭐ 而「询问而不假定」正是整个规范建立其上的模式。一个后端不定义它没有的那些
层的属性字,就使该模式在它最需要服务的那类平台上失效。

零是正确的值,而且已经是规范里写下的读法:「未赋值的位读作零,
以使一个按更晚规范编译的程序在更早的实现上行为正确」。
一台没有文件系统也没有调度器的机器,是这句话推到极限的情形。

⚠️ 读规范两轮没有发现这一条;写一个程序跑一次就挖出来了。
这在本生态里是同一教训的第三次。

Author: Sunrisepeak

src/kal.cpp

@@ -236,4 +236,32 @@ void* kal_alloc(kal_uintptr size, kal_uintptr align) {
 // rather than an omission.
 void kal_free(void*, kal_uintptr, kal_uintptr) {}
 
+// ── Capability words for the layers this machine does not have ──────────────
+//
+// ⚠️ A BACKEND MUST DEFINE EVERY PROPERTY WORD, INCLUDING THE ONES THAT READ
+// ZERO, OR THE QUESTION ITSELF FAILS TO LINK.
+//
+// The specification's queries are inline functions over these objects:
+//
+//     inline props properties() { return props{kal_fs_props}; }
+//
+// so a program that merely ASKS whether a filesystem exists takes the address
+// of `kal_fs_props`. Leaving it undefined on a machine that has no filesystem
+// makes the question unanswerable in the strongest sense: it does not link.
+//
+//     ld.lld: error: undefined symbol: kal_fs_props
+//     >>> referenced by fs.cppm:136
+//     >>>               obj/main.o:(kal::fs::properties@openkal.fs())
+//
+// Measured while porting a capability-querying program to this backend. The
+// program contained no filesystem call at all — the reference came from the
+// query, which is the pattern the whole specification is built on.
+//
+// Zero is the correct value and is already the specified reading: "an
+// unassigned position reads as zero, so that a program compiled against a later
+// specification behaves correctly against an earlier implementation". A machine
+// with no filesystem and no scheduler is that case taken to its limit.
+const kal_uintptr kal_fs_props   = 0;
+const kal_uintptr kal_task_props = 0;
+
 }  // extern "C"