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/hooks/generate.py

@@ -215,8 +215,16 @@ def validate(spec: dict) -> dict:
             raise SpecError(
                 f"hook {entry['id']!r} runs on {entry['event']} and must declare local_only: true"
             )
-        if not str(entry["command"]).startswith("mem0-agent "):
-            raise SpecError(f"hook {entry['id']!r}: command must invoke the mem0-agent CLI")
+        # Commands must invoke the plugin's own bundled launcher. A bare console script is
+        # not dependable: under pyenv the shim resolves against whichever Python version the
+        # current directory selects, so a repo pinning a different version fails with
+        # "pyenv: mem0-agent: command not found".
+        cmd = str(entry["command"])
+        if not cmd.startswith("${CLAUDE_PLUGIN_ROOT}/bin/mem0-agent "):
+            raise SpecError(
+                f"hook {entry['id']!r}: command must invoke "
+                "${CLAUDE_PLUGIN_ROOT}/bin/mem0-agent"
+            )
     return spec