feat(knowledge): auto-maintain index.md, improve import UX, fix embedding provider

- Auto-rebuild knowledge/index.md from the real directory tree on
  create/import so it never drifts or loses documents (no longer relies
  on the agent hand-writing it).
- Auto-open the created/imported document in the tree after success.
- Add create_document status message, shorten EN action buttons, and
  localize the "insert template" content.
- Show filename for protected system files (index.md/log.md) in the tree
  instead of their H1 heading.
- Reuse a shared embedding-provider factory so knowledge index sync also
  gets vectors instead of degrading to keyword-only search.

agent/memory/embedding/rebuild.py

@@ -163,10 +163,9 @@ def main() -> int:
     logger.info(f"[RebuildIndex] Workspace: {workspace_root}")
     logger.info(f"[RebuildIndex] Index db:  {memory_config.get_db_path()}")
 
-    from bridge.agent_initializer import AgentInitializer
+    from agent.memory.embedding import create_default_embedding_provider
 
-    initializer = AgentInitializer(bridge=None, agent_bridge=None)
-    embedding_provider = initializer._init_embedding_provider(memory_config, session_id=None)
+    embedding_provider = create_default_embedding_provider()
     if embedding_provider is None:
         logger.error(
             "[RebuildIndex] No embedding provider could be initialized. "