Update docx, xlsx, pdf, pptx skills with latest improvements (#330)

docx: Add commenting and track-changes support. Reorganize OOXML
tooling into a shared office/ module.

pptx: Streamline SKILL.md, add slide-editing and pptxgenjs guides,
bundle html2pptx as a tgz. Reorganize OOXML tooling into a shared
office/ module.

xlsx: Move recalc script into scripts/ and expand it. Add shared
office/ module for OOXML pack/unpack/validate.

pdf: Improve form-filling workflow with new form-structure extraction
script and updated field-info extraction.

skills/docx/scripts/office/schemas/ecma/fouth-edition/opc-relationships.xsd

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<xsd:schema xmlns="http://schemas.openxmlformats.org/package/2006/relationships"
+  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
+  targetNamespace="http://schemas.openxmlformats.org/package/2006/relationships"
+  elementFormDefault="qualified" attributeFormDefault="unqualified" blockDefault="#all">
+
+  <xsd:element name="Relationships" type="CT_Relationships"/>
+  <xsd:element name="Relationship" type="CT_Relationship"/>
+
+  <xsd:complexType name="CT_Relationships">
+    <xsd:sequence>
+      <xsd:element ref="Relationship" minOccurs="0" maxOccurs="unbounded"/>
+    </xsd:sequence>
+  </xsd:complexType>
+
+  <xsd:complexType name="CT_Relationship">
+    <xsd:simpleContent>
+      <xsd:extension base="xsd:string">
+        <xsd:attribute name="TargetMode" type="ST_TargetMode" use="optional"/>
+        <xsd:attribute name="Target" type="xsd:anyURI" use="required"/>
+        <xsd:attribute name="Type" type="xsd:anyURI" use="required"/>
+        <xsd:attribute name="Id" type="xsd:ID" use="required"/>
+      </xsd:extension>
+    </xsd:simpleContent>
+  </xsd:complexType>
+
+  <xsd:simpleType name="ST_TargetMode">
+    <xsd:restriction base="xsd:string">
+      <xsd:enumeration value="External"/>
+      <xsd:enumeration value="Internal"/>
+    </xsd:restriction>
+  </xsd:simpleType>
+</xsd:schema>