docs(manual): keep backticks out of verbatim blocks and off line breaks

Two shapes reach a reader as literal punctuation rather than markup:

A backtick inside a four-space block. The block is verbatim in every
renderer -- pandoc sets it monospace, prettify() fences it for the site
-- so the backtick is a character on the page. Twelve such lines are
cleaned; each sat at the start of its column, so the alignment of the
C5 capture table and the component summaries is unchanged.

A span split over a line break. Markdown pairs it happily, but
config-help pairs backticks one line at a time, so `fish-deps\nupdate`
showed both halves. The sentence is reflowed.

Both are now enforced, the first by test_concat_section_five_stays_
verbatim and the second by test_concat_code_spans_never_straddle_a_line.

docs/manual/09-fisher-plugins.md

@@ -120,7 +120,7 @@ The `fish_plugins` file at the config root:
 - [`jorgebucaran/fisher`](https://github.com/jorgebucaran/fisher) — Plugin manager itself
 - [`meaningful-ooo/sponge`](https://github.com/meaningful-ooo/sponge) — Remove failed commands from history
 
-To update all Fisher-managed plugins, run `fisher update` or `fish-deps
-update` which calls it as its first step.
+To update all Fisher-managed plugins, run `fisher update` or
+`fish-deps update` which calls it as its first step.
 
 ---