chore(cloud-tier): upgrade default model gemini-2.0-flash → gemini-2.5-flash

gemini-2.0-flash is deprecated June 1 2026. gemini-2.5-flash has been
stable since Q1 2026 with similar pricing ($0.15/$0.60 per 1M tokens
vs $0.10/$0.40 — pricing table already had the entry).

Three files touched:
- packages/shared-llm/src/backends/cloud.ts — client default
- services/mana-llm/src/config.py — server default
- services/mana-llm/src/providers/google.py — Ollama→Gemini fallback
  map + constructor default + deduplicated model list

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services/mana-llm/src/config.py

@@ -30,7 +30,7 @@ class Settings(BaseSettings):
 
     # Google Gemini (Fallback provider)
     google_api_key: str | None = None
-    google_default_model: str = "gemini-2.0-flash"
+    google_default_model: str = "gemini-2.5-flash"
 
     # Auto-fallback: Ollama → Google when Ollama is overloaded/down
     auto_fallback_enabled: bool = True