fix(mem0-agent): bundle a launcher so hooks never depend on a global CLI

SessionStart failed with 'pyenv: mem0-agent: command not found' in any repo whose
.python-version selects a Python the console script was not installed into. A
pip entry point is the wrong dependency for a plugin.

- bin/mem0-agent: POSIX launcher that picks the first CPython >= 3.10 it can find
  and runs the package from source (there are no third-party dependencies)
- hooks now invoke ${CLAUDE_PLUGIN_ROOT}/bin/mem0-agent, matching how the v1
  plugin calls its own scripts; the generator enforces this
- app_id override renamed to MEM0_AGENT_APP_ID: v1 exports MEM0_PROJECT_ID, which
  was silently overriding this plugin's project scope while both are installed

Verified: all six hooks exit 0 from a pyenv-3.11 repo, and app_id resolves per
repository again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

integrations/mem0-agent/tests/test_generate.py

@@ -48,7 +48,10 @@ def test_every_hook_declares_its_contract(spec):
         assert entry["why"], f"{entry['id']} must say why it exists"
         assert isinstance(entry["local_only"], bool)
         assert isinstance(entry["background"], bool)
-        assert entry["command"].startswith("mem0-agent ")
+        assert entry["command"].startswith("${CLAUDE_PLUGIN_ROOT}/bin/mem0-agent "), (
+            "hooks must call the plugin's bundled launcher, not a global console script "
+            "(a pyenv shim resolves against the directory's Python version and can vanish)"
+        )
 
 
 def test_tiny_parser_handles_quotes_comments_and_nesting():