fix(openrouter): respect the requesting user's saved model config

generatePostText ignored the userId it received and always read an
arbitrary row via getAnyOpenrouterConfig() (LIMIT 1, no ORDER BY),
so a model chosen and saved in Settings could be shadowed by another
stale config row. Now it prefers the requesting user's own config,
falling back to the most recently updated shared one. Also swap the
retired anthropic/claude-3.5-sonnet default for a live OpenRouter slug.

migration-docker.sql

@@ -88,7 +88,7 @@ CREATE TABLE IF NOT EXISTS openrouter_config (
   id VARCHAR PRIMARY KEY DEFAULT gen_random_uuid(),
   user_id VARCHAR NOT NULL UNIQUE REFERENCES users(id) ON DELETE CASCADE,
   api_key TEXT NOT NULL,
-  model TEXT NOT NULL DEFAULT 'anthropic/claude-3.5-sonnet',
+  model TEXT NOT NULL DEFAULT 'anthropic/claude-sonnet-4.5',
   system_prompt TEXT NOT NULL DEFAULT 'Tu es un expert en marketing des réseaux sociaux. Génère 3 variations de textes engageants pour des publications Facebook et Instagram à partir des informations produit fournies. Chaque variation doit être unique, captivante et optimisée pour l''engagement.',
   created_at TIMESTAMP DEFAULT NOW(),
   updated_at TIMESTAMP DEFAULT NOW()