feat(enc): Encaps E7 - c2 = byteEncode_dv(Compress_dv(v)) + end-to-end KAT

Reuses the E5 bit-packer FSM for ST_ENC_C2, generalized over region:
- coeff source: cp_coeff_src = bank_t[UPSUM] (v) for C2, bank_se (u) for C1
- bit width: cp_d already = dv_rt for C2 else du_rt
- poly count: cp_poly_max = 1 (single v) for C2, K for C1
- ct write pointer cp_wa CONTINUES from c1_bytes into C2 (not reset), so c2
  lands right after c1. c1 ends on a whole-byte/poly boundary (256*du/8
  integral), so cp_buf/nbits are empty at the C1->C2 handoff.

FSM tail: ST_ENC_V -> ST_ENC_C2 -> ST_DONE.

TB: verify_e7 compares the full ct (c1||c2, CTB bytes) to KAT.ct byte-exact
via the dbg_ct tap. Combined with the E0 ss==KAT.ss check this is the full
end-to-end Encaps KAT (ct==KAT.ct && ss==KAT.ss).

Verified end-to-end for K=2/3/4, cases 0-2 (K2) / 0-1 (K3,K4):
ct==KAT.ct && ss==KAT.ss. ML-KEM Encaps complete. KeyGen unregressed.

sync_rtl/top/TB/tb_mlkem_enc_katK_xsim.v

@@ -113,6 +113,8 @@ module tb_mlkem_enc_katK_xsim;
         // E5: c1 = byteEncode_du(Compress_du(u)) must equal KAT.ct[0..C1B-1].
         // Runs for every K/case (ct_b is the full KAT ciphertext).
         verify_e5;
+        // E7: full ct = c1 || c2 must equal KAT.ct (all CTB bytes). End-to-end.
+        verify_e7;
         $finish;
     end
 
@@ -244,4 +246,24 @@ module tb_mlkem_enc_katK_xsim;
             else         $display("K=2 CASE 0 FAIL (E6): %0d coeff mismatches", ce);
         end
     endtask
+
+    // E7: full ciphertext ct = c1 || c2 read from ct_bram (0..CTB-1) via dbg_ct
+    // tap; compare to KAT.ct byte-exact. This is the end-to-end Encaps check
+    // (ct == KAT.ct). ss == KAT.ss is already checked at E0.
+    task verify_e7;
+        integer be;
+        begin
+            be = 0;
+            for (i = 0; i < CTB; i = i + 1) begin
+                dbg_ct_idx_i = i[10:0];
+                @(posedge clk); @(posedge clk); @(posedge clk);
+                if (dbg_ct_o !== ct_b[i]) begin
+                    if (be < 8) $display("  CT[%0d] got=%02x exp=%02x", i, dbg_ct_o, ct_b[i]);
+                    be = be + 1;
+                end
+            end
+            if (be == 0) $display("K=%0d CASE %0d PASS (E7): ct (%0d B) == KAT.ct  [ct==KAT.ct && ss==KAT.ss]", KP, casenum, CTB);
+            else         $display("K=%0d CASE %0d FAIL (E7): %0d ct byte mismatches", KP, casenum, be);
+        end
+    endtask
 endmodule