fix: use CLAUDE_PLUGIN_ROOT for continuous-learning-v2 paths

Fixes #113

The instinct commands referenced hardcoded paths that only work with
manual installation (~/.claude/skills/...). When installed as a plugin,
files are at ~/.claude/plugins/cache/.../skills/...

Changes:
- Updated instinct-status, instinct-import, evolve commands to use
  ${CLAUDE_PLUGIN_ROOT} with fallback to manual path
- Updated observe.sh hook documentation with both install methods
- Updated SKILL.md with plugin vs manual installation instructions
- Removed duplicate commands from skills/continuous-learning-v2/commands/
  (already exist in commands/)

Users should use ${CLAUDE_PLUGIN_ROOT} in their hooks config when
installed as a plugin.

skills/continuous-learning-v2/hooks/observe.sh

@@ -5,15 +5,31 @@
 # Claude Code passes hook data via stdin as JSON.
 #
 # Hook config (in ~/.claude/settings.json):
+#
+# If installed as a plugin, use ${CLAUDE_PLUGIN_ROOT}:
 # {
 #   "hooks": {
 #     "PreToolUse": [{
 #       "matcher": "*",
-#       "hooks": [{ "type": "command", "command": "~/.claude/skills/continuous-learning-v2/hooks/observe.sh" }]
+#       "hooks": [{ "type": "command", "command": "${CLAUDE_PLUGIN_ROOT}/skills/continuous-learning-v2/hooks/observe.sh pre" }]
 #     }],
 #     "PostToolUse": [{
 #       "matcher": "*",
-#       "hooks": [{ "type": "command", "command": "~/.claude/skills/continuous-learning-v2/hooks/observe.sh" }]
+#       "hooks": [{ "type": "command", "command": "${CLAUDE_PLUGIN_ROOT}/skills/continuous-learning-v2/hooks/observe.sh post" }]
+#     }]
+#   }
+# }
+#
+# If installed manually to ~/.claude/skills:
+# {
+#   "hooks": {
+#     "PreToolUse": [{
+#       "matcher": "*",
+#       "hooks": [{ "type": "command", "command": "~/.claude/skills/continuous-learning-v2/hooks/observe.sh pre" }]
+#     }],
+#     "PostToolUse": [{
+#       "matcher": "*",
+#       "hooks": [{ "type": "command", "command": "~/.claude/skills/continuous-learning-v2/hooks/observe.sh post" }]
 #     }]
 #   }
 # }