docs(site): add inline code spans to generated Starlight pages

Function doc-headers are authored as plain text -- `config-help`,
`funcsave` and anyone opening the `.fish` file read them as-is -- so they
carry no backticks. The site inherited that and rendered `-a/--all` and
`__fish_config_op_aliases` as ordinary prose.

docs/codespans.py adds the spans at render time, as the last step of
prettify(), so only the site sees them; build_concat() (man page,
config-help) is byte-for-byte unchanged.

Recognised shapes: flags and flag pairs, `$vars`, SCREAMING_SNAKE env
vars, snake_case identifiers, paths and filenames, key chords, command
shadow chains (`ls->eza`), runs of tool names, whole command lines in a
table column of command lines, and known command names -- drawn from the
`_fdc_*` catalog in functions/_fish_deps_catalog.fish, the functions/
listing, and a standard-command list, minus the names that also read as
English.

Fenced blocks, existing code spans, headings, link targets, URLs,
component markup and <FileTree> bodies are passed through untouched, and
every rule bails out rather than guess.

docs/build-manual.py

@@ -8,12 +8,14 @@
 """
 
 import argparse
+import functools
 import json
 import re
 import shutil
 import sys
 from pathlib import Path
 
+import codespans
 import manualtools as mt
 import generate_component_registry
 
@@ -484,12 +486,21 @@ def _as_aside(para: list[str]) -> str | None:
     return f"<Aside {attrs}>\n{body}\n</Aside>"
 
 
+@functools.lru_cache(maxsize=1)
+def _code_vocabulary() -> codespans.Vocabulary:
+    """The command names codespans may wrap, read from the repo once."""
+    return codespans.vocabulary(DOCS.parent)
+
+
 def prettify(body: str, entry_name: str | None = None) -> str:
     """Rewrite a body's indented code blocks and labeled asides for the website.
 
     Site-only: the man page and `config-help` keep reading the untouched
     SSOT, where the indented form and the `LABEL:` text are exactly what
-    pandoc/`config-help` want.
+    pandoc/`config-help` want. The same applies to the inline code spans
+    added last: `-a/--all` and `__fish_config_op_aliases` are authored bare
+    so the `functions/*.fish` headers stay readable as plain text, and the
+    backticks the site wants are put on here rather than in the SSOT.
     """
     out: list[str] = []
     block: list[str] = []
@@ -528,7 +539,7 @@ def prettify(body: str, entry_name: str | None = None) -> str:
         while block and not block[-1].strip():
             block.pop()
         out.append(_prettify_block(block, entry_name))
-    return "\n".join(out)
+    return codespans.add_code_spans("\n".join(out), _code_vocabulary())
 
 
 ENTRY_HEADS = {