feat(docs): generate fish-config.md from the manual tree

Adds docs/build-manual.py (--concat) and a round-trip test in
verify-manual.py that reproduces the pre-migration fish-config.md
exactly from docs/manual/.

Fixes found by the round-trip check, applied in split-manual.py and
re-run to regenerate docs/manual/:
- NAME/SYNOPSIS/TABLE OF CONTENTS had no sidebar.order, so they sorted
  after every numbered section instead of interleaving with DESCRIPTION
  in original document order. All manual pages now get sidebar.order
  from a single position counter matching source order.
- split_h1/split_h2 used .strip() on section bodies, which also ate
  leading indentation on the first body line, corrupting the 4-space
  indented code blocks that open SYNOPSIS and TABLE OF CONTENTS.
- The source's leading pandoc metadata block (title/section/header/
  date/author) was discarded entirely by the splitter. It's now parsed
  off via manualtools.parse and stashed on index.md under a "pandoc"
  key; build-manual.py re-emits it verbatim ahead of the first heading.

docs/manual/00-name.md

@@ -3,6 +3,8 @@ title: Name
 manTitle: NAME
 man: true
 site: false
+sidebar:
+  order: 1
 ---
 
 fish-config - personal fish shell configuration for Fish 4.x with modern CLI tool integration

docs/manual/00-synopsis.md

@@ -3,9 +3,11 @@ title: Synopsis
 manTitle: SYNOPSIS
 man: true
 site: false
+sidebar:
+  order: 2
 ---
 
-help config [SECTION]
+    help config [SECTION]
 
 Open this manual in the best available pager. Optionally jump to a section
 by keyword:

docs/manual/00-table-of-contents.md

@@ -3,9 +3,11 @@ title: Table Of Contents
 manTitle: TABLE OF CONTENTS
 man: true
 site: false
+sidebar:
+  order: 4
 ---
 
-1.  Configuration Variables
+    1.  Configuration Variables
     2.  PATH Setup
     3.  Key Bindings
     4.  Abbreviations

docs/manual/01-configuration-variables.md

@@ -2,7 +2,7 @@
 title: Configuration Variables
 manTitle: 1. CONFIGURATION VARIABLES
 sidebar:
-  order: 1
+  order: 5
 helpKeywords:
 - variables
 - config

docs/manual/02-path-setup.md

@@ -2,7 +2,7 @@
 title: Path Setup
 manTitle: 2. PATH SETUP
 sidebar:
-  order: 2
+  order: 6
 helpKeywords:
 - path
 ---

docs/manual/03-key-bindings.md

@@ -2,7 +2,7 @@
 title: Key Bindings
 manTitle: 3. KEY BINDINGS
 sidebar:
-  order: 3
+  order: 7
 helpKeywords:
 - keybindings
 - bindings

docs/manual/04-abbreviations.md

@@ -2,7 +2,7 @@
 title: Abbreviations
 manTitle: 4. ABBREVIATIONS
 sidebar:
-  order: 4
+  order: 8
 helpKeywords:
 - abbreviations
 - abbr

docs/manual/05-functions/index.md

@@ -2,7 +2,7 @@
 title: Functions Reference
 manTitle: 5. FUNCTIONS REFERENCE
 sidebar:
-  order: 5
+  order: 9
 helpKeywords:
 - functions
 ---

docs/manual/06-dependency-catalog.md

@@ -2,7 +2,7 @@
 title: Dependency Catalog
 manTitle: 6. DEPENDENCY CATALOG
 sidebar:
-  order: 6
+  order: 10
 helpKeywords:
 - catalog
 - deps-catalog

docs/manual/07-customization.md

@@ -2,7 +2,7 @@
 title: Customization
 manTitle: 7. CUSTOMIZATION
 sidebar:
-  order: 7
+  order: 11
 helpKeywords:
 - customization
 - customize

docs/manual/08-fisher-plugins.md

@@ -2,7 +2,7 @@
 title: Fisher Plugins
 manTitle: 8. FISHER PLUGINS
 sidebar:
-  order: 8
+  order: 12
 helpKeywords:
 - plugins
 - fisher

docs/manual/09-installation.md

@@ -2,7 +2,7 @@
 title: Installation
 manTitle: 9. INSTALLATION
 sidebar:
-  order: 9
+  order: 13
 helpKeywords:
 - installation
 - install

docs/manual/10-personalization.md

@@ -2,7 +2,7 @@
 title: Personalization
 manTitle: 10. PERSONALIZATION
 sidebar:
-  order: 10
+  order: 14
 helpKeywords:
 - personalization
 - personalize

docs/manual/11-viewing-this-manual.md

@@ -2,7 +2,7 @@
 title: Viewing This Manual
 manTitle: 11. VIEWING THIS MANUAL
 sidebar:
-  order: 11
+  order: 15
 helpKeywords:
 - viewing
 - manual

docs/manual/index.md

@@ -3,7 +3,13 @@ title: Fish Shell Configuration
 description: Reference manual for the rootiest fish configuration.
 manTitle: DESCRIPTION
 sidebar:
-  order: 0
+  order: 3
+pandoc:
+  title: FISH-CONFIG
+  section: 7
+  header: Fish Shell Configuration User Manual
+  date: June 2026
+  author: Rootiest
 helpKeywords:
 - description
 - autopair