fix(cli): honor env precedence for LLM and run config

Interactive selections and flag defaults overrode TRADINGAGENTS_* env vars.
Rule: an explicit env value or CLI flag wins; otherwise the env-applied
default is kept.

- Research depth: skip the prompt when both round-count env vars are set, and
  stop overwriting them (#977).
- Checkpoint: --checkpoint/--no-checkpoint is tri-state; omitting it keeps
  TRADINGAGENTS_CHECKPOINT_ENABLED (#976).
- Docker ollama: use TRADINGAGENTS_LLM_PROVIDER + OLLAMA_BASE_URL, not a bare
  LLM_PROVIDER the overlay never reads (#975).
- Reasoning/thinking knobs: settable via env; the prompt is skipped when set.
- Effort gating: forward effort only to models that accept it (Anthropic
  Opus 4.5+/Sonnet 4.6+, OpenAI reasoning models); drop it elsewhere.
- Boolean env values: raise a named error on invalid input instead of
  silently becoming False.

.env.example

@@ -55,3 +55,8 @@ NVIDIA_API_KEY=
 # honor it). Unset leaves each provider at its default. See the README
 # "Reproducibility" note — no setting makes LLM output fully deterministic.
 #TRADINGAGENTS_TEMPERATURE=0.0
+# Provider-specific reasoning/thinking depth (optional; unset = provider
+# default). Setting one also skips the matching interactive prompt.
+#TRADINGAGENTS_OPENAI_REASONING_EFFORT=medium
+#TRADINGAGENTS_GOOGLE_THINKING_LEVEL=high
+#TRADINGAGENTS_ANTHROPIC_EFFORT=high