Port Windows installer/ncp fixes and a real nomic-embed-text default

- install-windows.ps1: warn about a leftover profile-based ncp() that
  would shadow ncp.cmd; the "press any key to close" footer now skips
  the wait when stdin is redirected (was hanging indefinitely) and
  exits cleanly instead of Stop-Process when it owns the window; pulls
  nomic-embed-text alongside the chat/memory models.
- management/ncp.py: ncp start / start -b bring Ollama up automatically;
  longer timeout + real error message on a slow model warm.
- synapse/nexus_config.py: DEFAULT_EMBED_MODEL, single source of truth
  alongside DEFAULT_CHAT_MODEL/DEFAULT_MEMORY_MODEL.
- synapse/ollama_manager.py: is_available() cached instead of spawning a
  process per /status poll; is_running() timeout dropped 2s -> 0.5s so a
  healthy backend stops reading as dead; embed() reads the new default
  instead of a hardcoded string; de-duplicated serve-env setup.

Ported via bin/publish.sh from NexusOS-jon.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

synapse/nexus_config.py

@@ -22,7 +22,7 @@ except Exception:
     VERSION = "0.0.0"
 
 # --- MODEL DEFAULTS ---
-# Single source of truth for the two models NexusOS ships with. The installers
+# Single source of truth for the three models NexusOS ships with. The installers
 # pull and pin these, the runtime falls back to them; keeping them in one place
 # is what stops installer and backend from drifting apart.
 #
@@ -30,8 +30,12 @@ except Exception:
 # 4 GB GPU into CPU/RAM). Chosen over Qwen3 because Qwen3 is a reasoning model:
 # smart only with its slow <think> step, weak without it.
 # Memory: mistral - the curator that extracts facts and titles conversations.
+# Embed: nomic-embed-text - powers semantic recall of past conversations
+# (OllamaManager.embed / store.semantic_search_conversations). Without it,
+# recall silently degrades to lexical substring matching.
 DEFAULT_CHAT_MODEL = "llama3.1:8b"
 DEFAULT_MEMORY_MODEL = "mistral:latest"
+DEFAULT_EMBED_MODEL = "nomic-embed-text"
 
 # --- CORE DIRECTORIES ---
 DATA_DIR = PROJECT_ROOT / "data"
@@ -144,7 +148,7 @@ settings = Settings()
 
 # explicit exports for static checkers and IDEs
 __all__ = ["Settings", "settings", "path", "VERSION",
-           "DEFAULT_CHAT_MODEL", "DEFAULT_MEMORY_MODEL",
+           "DEFAULT_CHAT_MODEL", "DEFAULT_MEMORY_MODEL", "DEFAULT_EMBED_MODEL",
            "PROJECT_ROOT", "DATA_DIR", "MODELS_DIR", "RUNTIME_DIR",
            "MEMORY_DIR", "LOGS_DIR", "PLAYBOOK_DIR", "UPLOADS_DIR",
            "EXPORTS_DIR", "MEMORY_DB",