fix-broken-link-xas (#1562)

## Issue
- Incorrect link format in XAS demo
- Reported on QA channel -
[link](https://xanaduhq.slack.com/archives/C05C2NU8QBY/p1759160279171989)

## Preview
- https://pennylane.ai/qml/demos/tutorial_xas?pr=1562

## Testing

- Check that link to `How to build compressed double-factorized
Hamiltonians` & `Initial state preparation for quantum chemistry` works
<img width="829" height="231" alt="Screenshot 2025-09-29 at 12 06 32 PM"
src="https://github.com/user-attachments/assets/4cf06183-378b-429c-80b1-aacaa822ddd8"
/>

Author: ashishks0522

demonstrations_v2/tutorial_xas/demo.py

@@ -143,7 +143,7 @@
 Ground state calculation
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-If you haven’t, check out the demo `“Initial state preparation for quantum chemistry” <demos/tutorial_initial_state_preparation>`__. 
+If you haven’t, check out the demo :doc:`Initial state preparation for quantum chemistry <demos/tutorial_initial_state_preparation>`. 
 We will be expanding on that demo with code to import a state from the `complete active space configuration interaction <https://pyscf.org/user/mcscf.html>`__ (CASCI) methods of PySCF, where we restrict the set of active orbitals used in the calculation. 
 
 We start by creating our molecule object using the `Gaussian type orbitals <https://en.wikipedia.org/wiki/Gaussian_orbital>`__ module ``pyscf.gto``, and obtaining the Hartree-Fock molecular orbitals with the `self-consistent field methods <https://pyscf.org/user/scf.html>`__ ``pyscf.scf``.
@@ -317,7 +317,7 @@ def initial_circuit(wf):
 # Next we will discuss how to prepare the electronic Hamiltonian for efficient time evolution in the Hadamard test circuit. 
 # We will perform compressed double factorization (CDF) on the Hamiltonian to approximate it as a series of fragments, each of which can be fast-forwarded in a Trotter product formula.
 #
-# If you haven’t yet, go read the demo `“How to build compressed double-factorized Hamiltonians” <demos/tutorial_how_to_build_compressed_double_factorized_hamiltonians>`__, because that is exactly what we are going to do! 
+# If you haven’t yet, go read the demo :doc:`How to build compressed double-factorized Hamiltonians <demos/tutorial_how_to_build_compressed_double_factorized_hamiltonians>`, because that is exactly what we are going to do!
 # You could also look at Section III in Ref. [#Fomichev2025]_.
 #
 # Electronic Hamiltonian

demonstrations_v2/tutorial_xas/metadata.json

@@ -11,7 +11,7 @@
     "executable_stable": true,
     "executable_latest": true,
     "dateOfPublication": "2025-08-29T09:00:00+00:00",
-    "dateOfLastModification": "2025-09-22T15:48:14+00:00",
+    "dateOfLastModification": "2025-09-30T15:48:14+00:00",
     "categories": [
         "Quantum Chemistry",
         "Algorithms"