fix(spreadsheetbench)+optimizer: fix verify-feedback bloat, drop optimizer-side truncation, soft-disable gate

A. SpreadsheetBench verification-feedback bloat
   - rollout.py _auto_verify_output: use official _compare_cell_value (was
     repr() equality, which falsely flagged 5 vs 5.0 / None vs ""); collapse
     correct-and-empty cells into a count so large sparse answer ranges no
     longer flood feedback with MBs of None=None noise.
   - codegen_agent.py _build_eval_feedback: only list WRONG cells, collapse
     correct ones into a count.
   Scoring is unaffected (evaluate() is independent); this only fixes the
   target model's multi-turn solving feedback.

B. Remove optimizer-side truncation (bloat source now fixed)
   - reflect.py: drop _MAX_TRAJ_CHARS cap and all per-field clips.
   - update_modes.py / clip.py / lr_autonomous.py: describe_item /
     short_item_summary no longer truncate; raise ranking/lr token budget.
   - trainer.py _format_step_buffer: full task_ids / target.
   - slow_update.py: full comparison samples.

C. Soft-disable gate
   - config.py / trainer.py: use_gate=false no longer raises; validation still
     runs but candidates are force-accepted (new force_accept branch + log).

Misc: aggregate.py merge token budget 4096 -> 16384.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

skillopt/optimizer/lr_autonomous.py

@@ -48,7 +48,7 @@ def decide_autonomous_learning_rate(
     items = get_payload_items(merged_patch, update_mode)
     available = len(items)
     item_lines = [
-        f"[{idx}] {describe_item(item, update_mode, max_chars=700)}"
+        f"[{idx}] {describe_item(item, update_mode)}"
         for idx, item in enumerate(items)
     ]
     user = (
@@ -76,7 +76,7 @@ def decide_autonomous_learning_rate(
         response, _ = chat_optimizer(
             system=load_prompt("lr_autonomous"),
             user=user,
-            max_completion_tokens=2048,
+            max_completion_tokens=16384,
             retries=3,
             stage="lr_autonomous",
         )