feat: unified drafts/ structure with PDF outputs for ACT and ECT

Both drafts now live in workspace/drafts/ as siblings:
  drafts/
  ├── act/                       (ACT -01, native to parent repo)
  │   ├── draft-nennemann-act-01.md     kramdown-rfc source
  │   ├── draft-nennemann-act-01.{xml,txt,html,pdf}
  │   ├── .refcache/             bibxml cache
  │   └── build.sh
  ├── ietf-wimse-ect/            (ECT -02, submodule, PDF added)
  │   └── ...
  └── README-pdf.md              PDF toolchain docs

ACT kramdown-rfc conversion:
- full YAML frontmatter (title, author, refs)
- section structure matches kramdown-rfc conventions
- {{REF}} citation syntax, auto-numbered sections
- references auto-built from normative/informative blocks
- removed manual TOC (kramdown-rfc generates)
- builds cleanly: 133K XML, 89K TXT, 208K HTML, 167K PDF

PDF toolchain:
- xml2rfc --pdf via weasyprint<60 + pydyf<0.10 injected into xml2rfc pipx venv
- both build.sh scripts now produce PDF as Step 4
- README-pdf.md documents the setup for new machines

Submodule: bump ietf-wimse-ect pointer for build.sh PDF step

workspace/drafts/act/.refcache/reference.RFC.9110.xml

@@ -0,0 +1,16 @@
+<reference anchor="RFC9110" target="https://www.rfc-editor.org/info/rfc9110">
+  <front>
+    <title>HTTP Semantics</title>
+    <author fullname="R. Fielding" initials="R." role="editor" surname="Fielding"/>
+    <author fullname="M. Nottingham" initials="M." role="editor" surname="Nottingham"/>
+    <author fullname="J. Reschke" initials="J." role="editor" surname="Reschke"/>
+    <date month="June" year="2022"/>
+    <abstract>
+      <t>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes.</t>
+      <t>This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230.</t>
+    </abstract>
+  </front>
+  <seriesInfo name="STD" value="97"/>
+  <seriesInfo name="RFC" value="9110"/>
+  <seriesInfo name="DOI" value="10.17487/RFC9110"/>
+</reference>