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/src/mem0_agent/settings.py

@@ -170,7 +170,9 @@ def resolve_app_id(cwd: str | None = None, settings: Settings | None = None) ->
     env override -> cwd map -> remote-hash map (self-healing after a move)
     -> owner-repo slug -> directory name.
     """
-    override = os.environ.get("MEM0_PROJECT_ID")
+    # Deliberately NOT MEM0_PROJECT_ID: the v1 plugin exports that, and while both are
+    # installed it would silently override this plugin's project scope.
+    override = os.environ.get("MEM0_AGENT_APP_ID")
     if override:
         return override.strip()
     cwd = cwd or os.getcwd()