Update docx, xlsx, pdf, pptx skills with latest improvements

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/pptx/scripts/office/schemas/ISO-IEC29500-4_2016/shared-additionalCharacteristics.xsd

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="utf-8"?>
+<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
+  xmlns="http://schemas.openxmlformats.org/officeDocument/2006/characteristics"
+  targetNamespace="http://schemas.openxmlformats.org/officeDocument/2006/characteristics"
+  elementFormDefault="qualified">
+  <xsd:complexType name="CT_AdditionalCharacteristics">
+    <xsd:sequence>
+      <xsd:element name="characteristic" type="CT_Characteristic" minOccurs="0"
+        maxOccurs="unbounded"/>
+    </xsd:sequence>
+  </xsd:complexType>
+  <xsd:complexType name="CT_Characteristic">
+    <xsd:attribute name="name" type="xsd:string" use="required"/>
+    <xsd:attribute name="relation" type="ST_Relation" use="required"/>
+    <xsd:attribute name="val" type="xsd:string" use="required"/>
+    <xsd:attribute name="vocabulary" type="xsd:anyURI" use="optional"/>
+  </xsd:complexType>
+  <xsd:simpleType name="ST_Relation">
+    <xsd:restriction base="xsd:string">
+      <xsd:enumeration value="ge"/>
+      <xsd:enumeration value="le"/>
+      <xsd:enumeration value="gt"/>
+      <xsd:enumeration value="lt"/>
+      <xsd:enumeration value="eq"/>
+    </xsd:restriction>
+  </xsd:simpleType>
+  <xsd:element name="additionalCharacteristics" type="CT_AdditionalCharacteristics"/>
+</xsd:schema>