starkernel: item 4.1 -- hot words onto the Stadium, density-ranked eviction

Punch list §25 item 4.1 complete.
Replaces the round-robin hotwords cache with Stadium density-ranked
admission/eviction on the kernel side, via the §17.7 reservoir mechanism and a
kernel-side word_id -> cell_index map (no DictEntry change, dict_hash
untouched). Adds stadium_birth_hera() to close the cell-0 panic hazard,
STADIUM_WORD_HEAT_QUANTUM/STADIUM_WORD_COOL_RATE_Q48 Kconfig knobs (flagged
untuned), and a stadium_word_forget() FORGET coherence hook to close a
recycled-word_id aliasing gap.

Verified: all five hotwords_cache_* call sites in dictionary_management.c
bypassed under __STARKERNEL__; word dispatch feeds the Stadium at all three
vm_core.c physics_execution_heat_increment() sites; hosted make unaffected;
all three architectures booted to ok> with matching dict_hash
(0x3d4e1daf289da94f) and matching conservation stats (promotions=354
evictions=0, resident_sum=65536 reservoir=0 sum=65536).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/starkernel/kernel_main.c

@@ -53,6 +53,7 @@ EFI_RUNTIME_SERVICES *g_sk_runtime_services = NULL;
 #include "starkernel/vm/bootstrap/sk_vm_bootstrap.h"
 #include "starkernel/vm/parity.h"
 #include "starkernel/vm/stadium.h"
+#include "starkernel/vm/stadium_words.h"
 #include "starkernel/capsule_generated.h"
 #include "starkernel/capsule_loader.h"
 #include "starkernel/capsule_birth.h"  /* capsule_birth_mama, capsule_find_mama_init */
@@ -484,6 +485,14 @@ static void kernel_main_deep(BootInfo *boot_info) {
      * yet, so a failed allocation logs and boot continues. */
     (void)stadium_boot_init();
 
+    /* item 4.1, FABRIC.md item 3.6/§17.7: actually enforce "Hera is patron
+     * zero" before anything else can land on cell 0 via the free list, then
+     * bring up the word layer's map. Both must happen before the first word
+     * ever dispatches -- capsule birth below runs init.4th, which dispatches
+     * words. */
+    (void)stadium_birth_hera();
+    stadium_words_init();
+
     /* M7: VM Bootstrap and Parity Validation */
     console_println("VM: bootstrap parity...");
     ParityPacket parity_pkt;
@@ -614,6 +623,11 @@ static void kernel_main_deep(BootInfo *boot_info) {
 #ifdef STARFORTH_ENABLE_VM
     VM *mama = (VM *)sk_get_mama_vm();
 
+    /* item 4.1 diagnostic (§25.5 acceptance: "observable via a diagnostic
+     * word or boot console output"): word patrons already dispatched during
+     * capsule birth above, so this is non-vacuous by this point. */
+    stadium_words_print_boot_diagnostics(vm_uuid_hera());
+
     /*
      * Runtime --doe flag: inject "EXEC-DOE BYE" if requested via boot args.
      * Checked before SK_STARTUP_FORTH so a runtime --doe takes precedence.