docs(functions): merge remaining manual-only facts into headers

Word-level diff of every manual entry against its generated counterpart
surfaced 546 tokens present in the manual and absent from the header —
losses reconcile.py missed, because it compared description length and
these headers are longer overall thanks to ARGUMENTS/RETURNS.

Merged the substantive ones (546 -> 202 residual tokens, the remainder
being synonym drift). Notable real fixes:

- git-clean: -f/--force was missing from ARGUMENTS entirely
- pkg: per-package-manager query table
- qc: cli-role rationale, role paths, --role passthrough
- config-help: site URL, xdg-open, man page path, case-insensitivity
- agents-init: idempotency, .gitignore paths, upstream pull, wrapper callers
- smart_exit: exit-builtin wiring note, $SCROLLBACK_HISTORY_DIR

The manual's claim that claude/agy pass `agents-init --agents` is stale;
both pass `--quiet` (full setup). Header wins, manual dropped.

functions/open-url.fish

@@ -14,7 +14,8 @@
 #   binary rather than deferring to xdg-open, whose MIME dispatch can hand
 #   local text/html files to non-browser apps (e.g. ebook readers).
 #
-#   Silent by default: prints nothing on success (errors always go to stderr).
+#   Silent by default: prints nothing on success (errors always go to stderr);
+#   --silent / -s is accepted for explicitness.
 #
 #   Resolution order:
 #     1. $fish_help_browser  (explicit override)
@@ -38,6 +39,8 @@
 #   open-url -v https://fish-config-docs.pages.dev/
 #
 # NOTES
+#   Used internally by config-help --html.
+#
 #   Typo abbreviation: url-open (expands to open-url on space/enter).
 function open-url --description 'Open a URL in the best available web browser'
     argparse h/help s/silent v/verbose -- $argv