fix(completions): force --no-paging on bat invocations in completion scripts (#3760)

Every shell completion script (bash, zsh, fish, PowerShell) shells out
to bat to enumerate languages/themes for tab completion candidates. If
the user has wired bat into LESSOPEN (e.g. LESSOPEN='|-bat -f -pp %s'),
bat's normal pager auto-detection can engage when stdout looks like a
terminal at completion time and reflect ANSI escape sequences back into
the candidate list. The result is the issue's reproducer: tab completion
expands 'Per' to '\033[38;2;248;248;242mPerl' instead of 'Perl'.

The list-languages/list-themes calls are always meant to be machine-
readable, so they should never page. Pass --no-paging explicitly to
every bat invocation inside the four completion files. The flag is the
public alias for --paging=never (already documented in bat --help) and
is the same form completion scripts elsewhere in the codebase use.

Touches the four completion files only; no production code changes.

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Syntax highlighting for Python files using uv as script runner in shebang #3689 (@janlarres)
 
 ## Bugfixes
+- Pass `--no-paging` to `bat` invocations inside the bash / zsh / fish / PowerShell shell completion scripts so that shell-level pager wiring (e.g. `LESSOPEN='|-bat -f -pp %s'`) cannot inject ANSI escape sequences into the completion candidates. Closes #3760 (@mvanhorn)
 - Quote filenames before substituting them into `$LESSOPEN` / `$LESSCLOSE` templates, preventing shell injection when a filename contains shell metacharacters, see #3726 (@curious-rabbit)
 - Fix `--list-themes` unconditionally probing the terminal via OSC 10/11 even when `--theme` was set to an explicit value, see #3700 (regression introduced in bc42149a). (@optimistiCli)
 - Fix inverted `$LESSCLOSE` warning so bat warns on nonzero exit, not on success. See #3654 (@cuiweixie)