feat(logging)!: make C5 session logging opt-in

Session logging is the one opinionated category that writes a persistent
record of terminal output to disk, and those logs can contain secrets.
Silent-by-default is the wrong posture for it, so C5 now defaults to off:
__fish_config_op_logging must be set to an explicit truthy value to enable
capture, and the master switch cannot enable it on its own.

Implemented as a single special case in __fish_config_op_enabled, so all
five capture components, the sentinel file, the paru/yay wrappers, the
Kitty watcher, and the config-settings TUI pick it up with no other code
changes. The existing startup sync in conf.d/logging-events.fish
reconciles the sentinel and removes the generated wrappers on the first
shell after upgrading.

BREAKING CHANGE: users relying on the previous default must now run
`set -U __fish_config_op_logging on`. Existing logs in ~/.terminal_history
are left untouched.

config.fish

@@ -15,8 +15,11 @@
 #   __fish_config_op_overrides     C3 — key bindings, env, prompt overrides
 #   __fish_config_op_integrations  C4 — terminal/tool coupling
 #   __fish_config_op_logging       C5 — scrollback capture / AUR log wrappers
+#                                       (opt-in: unset means OFF)
 #   __fish_config_op_greeting      C6 — per-session greeting / first-run welcome
 # Example: set -U __fish_config_op_aliases off   (erase to re-enable)
+# C5 is the one exception: it defaults to disabled and needs an explicit
+# truthy value — set -U __fish_config_op_logging on
 
 #   ──────────────────────── Source CachyOS configs ────────────────────────
 if test -f /usr/share/cachyos-fish-config/cachyos-config.fish