fix: prevent internal prompts and duplicates in memory database

- Add server-side detection of SDK processor's internal system prompt
  in handleSessionInit, since CLAUDE_MNEMONIC_INTERNAL env var is not
  propagated by Claude Code to hook subprocesses
- Add cross-session duplicate detection (FindRecentPromptByTextGlobal)
  to catch same prompt text arriving from different session IDs
- Add hooks, mcpServers, and commands references to plugin.json per
  Claude Code plugin spec
- Remove MCP server injection from register-plugin.sh (now in plugin.json)
- Use ${CLAUDE_PLUGIN_ROOT} for statusline path instead of hardcoded path
- Add python3 fallback for plugin registration when jq is unavailable
- Replace hardcoded 1.0.0 version in findWorkerBinary with glob lookup
- Add cache copy verification in register-plugin.sh
- Add update-version Makefile target to keep metadata in sync

internal/worker/sdk/processor.go

@@ -696,7 +696,12 @@ func (p *Processor) callClaudeCLI(ctx context.Context, prompt string) (string, e
 	// (hooks are triggered based on working directory)
 	cmd.Dir = "/tmp"
 
-	// Disable any plugin hooks by setting an env var that our hooks can check
+	// Disable any plugin hooks by setting an env var that our hooks can check.
+	// NOTE: This env var is NOT reliably propagated to hook subprocesses because
+	// Claude Code constructs its own environment for hooks. The server-side check
+	// in handleSessionInit (handlers_sessions.go) provides the reliable guard by
+	// detecting the system prompt signature in the prompt text. This env var is
+	// kept as a best-effort defense-in-depth measure for cases where it does work.
 	cmd.Env = append(os.Environ(), "CLAUDE_MNEMONIC_INTERNAL=1")
 
 	// Capture output with size limits to prevent unbounded memory usage