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/cat.fish

@@ -8,9 +8,10 @@
 #   cat [args...]
 #
 # DESCRIPTION
-#   Enhanced cat replacement that uses bat for file display, runs ls when given
-#   a directory, falls back to raw cat for ANSI-colored log files, and finally
-#   falls back to standard cat if bat is not installed.
+#   Enhanced cat replacement. Wraps bat for files, giving syntax highlighting
+#   and line numbers; passes directories to ls; falls back to raw cat for
+#   ANSI-colored log files, and finally to /usr/bin/cat if bat is not
+#   installed.
 #
 # ARGUMENTS
 #   args...  Files or directories to display