fix: upsert DO NOTHING when updateCols empty, title model uses tabular model for Ollama

Two bugs:

1. PgAdapter upsert with only the conflict column (e.g. upsert({ user_id })
   on conflict user_id) produced "DO UPDATE SET " with an empty SET
   clause - invalid SQL. Now falls through to DO NOTHING when updateCols
   is empty, and supports the Supabase ignoreDuplicates:true option.
   This fixed "syntax error at end of input" on ensureProfileRow calls.

2. resolveTitleModel checked "apiKeys.ollama !== undefined" to detect
   Ollama, but the apiKeys object always initialises ollama: null (not
   undefined), so the condition was always true - every user with no cloud
   keys got title_model = local-gemma-26b which doesn't exist on Ollama.
   Fixed to check hasEnvOllama() || key.trim(), and when Ollama is the
   provider, reuse the user's configured tabular model (which they know is
   installed) instead of a hardcoded default.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>