fix: keep session lists user-facing

[epodivilov]

What

• filter child, subagent, and ephemeral Codex threads at the adapter boundary
• remove injected context/resource/environment blocks from fallback titles
• derive a human-authored title from history when the list preview contains only injected context
• return a neutral title when no meaningful human text is available

Why

Codex stores top-level conversations and internal worker threads together. Exposing the raw store through ACP makes internal sessions appear resumable and leaks transport context into session titles.

How

The list request continues to restrict provider source kinds, then applies defensive filtering using thread metadata. Title cleanup stays provider-local and reads history only for untitled rows whose preview contains no usable text after context removal.

Refs: ACP-290

Verification

• npm run typecheck
• npm test
• npm run build
• targeted list-session tests

Not verified

• Live npm run test:e2e: this environment has neither CODEX_API_KEY nor OPENAI_API_KEY.
• Installed adapter update/restart and comparison against the real shared Codex store.
• Manual load of CLI, Kepler, and active-writer sessions through the unified client.