chore(caveman): purge plugin + always-on integration

Disable + uninstall caveman@caveman and delete every repo dependency on
it: SessionStart/UserPromptSubmit hook blocks, standalone hook files,
settings.json enabledPlugins + marketplace entries, install-plugins.sh
STEP 5.5, update-all.sh refresh step, plugins.lock.json entry, doctor.sh
checks, lib/detect-plugins.sh helpers, lib/profile.sh + plugin-advisor +
skills/profile protected-list entries, .gitignore runtime-file block,
and README/USAGE docs. Dead /caveman:compress refs replaced with
manual/claude.ai guidance. Memory-registry terse-format convention kept
(separate subsystem). Version 3.4.0 -> 3.5.0.

On a subscription plan caveman's ~75% output-token compression has no
cost benefit, and the always-on hooks added friction on validation
gates and client deliverables.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X3e8LaH2vymmxyh36h3jFU

hooks/session-start.sh

@@ -131,7 +131,6 @@ ALWAYS_ON=()
 detect_rtk &>/dev/null && ALWAYS_ON+=("rtk")
 plugin_enabled "security-guidance@claude-code-plugins"  && ALWAYS_ON+=("security-guidance")
 plugin_enabled "superpowers@superpowers-marketplace"    && ALWAYS_ON+=("superpowers")
-plugin_enabled "caveman@caveman"                        && ALWAYS_ON+=("caveman")
 ALWAYS_ON_STR="${ALWAYS_ON[*]:-none}"
 # Same 40-char-width split policy as the toggle row below — keeps the
 # right border aligned when 4 always-on plugins overflow the field.