Replace ALLOT/comma/C-comma/ALIGN + float alignment with Forth (Phase 8)

Move memory allocation words to boot.fth:
- ALLOT: `: ALLOT HERE + 12 ! ;`
- , (comma): `: , HERE ! 1 CELLS ALLOT ;`
- C, : `: C, HERE C! 1 ALLOT ;`
- ALIGN: `: ALIGN HERE ALIGNED 12 ! ;`
- FALIGN, SFALIGN, DFALIGN: float-aligned variants

These write directly to WASM memory[SYSVAR_HERE]. The Rust side picks up
Forth-side HERE changes via refresh_user_here() which now reads both
here_cell (for Rust host functions) and memory[12] (for Forth words),
taking the maximum to ensure no allocation is lost.

Removed 222 lines of Rust. All 426 tests pass.

crates/core/boot.fth

@@ -160,6 +160,18 @@
 
 \ ALIGNED is already an IR primitive in the compiler.
 
+\ ALLOT ( n -- )  advance HERE by n bytes
+: ALLOT  HERE + 12 ! ;
+
+\ , ( x -- )  store cell at HERE, advance by cell
+: ,  HERE ! 1 CELLS ALLOT ;
+
+\ C, ( char -- )  store byte at HERE, advance by 1
+: C,  HERE C! 1 ALLOT ;
+
+\ ALIGN ( -- )  align HERE to cell boundary
+: ALIGN  HERE ALIGNED 12 ! ;
+
 \ ---------------------------------------------------------------
 \ Phase 5: I/O, pictured numeric output, formatted output
 \ ---------------------------------------------------------------
@@ -275,4 +287,13 @@
 \ DFALIGNED ( addr -- addr )  align to 8-byte double-float boundary
 : DFALIGNED  7 + -8 AND ;
 
+\ FALIGN ( -- )  align HERE to 8-byte float boundary
+: FALIGN  HERE FALIGNED 12 ! ;
+
+\ SFALIGN ( -- )  align HERE to 4-byte single-float boundary
+: SFALIGN  ALIGN ;
+
+\ DFALIGN ( -- )  align HERE to 8-byte double-float boundary
+: DFALIGN  FALIGN ;
+
 \ .S keeps its Rust host function (complex stack introspection).