Relock in2lambda and offer field set and part solution to the fix loop

[peterbjohnson]

in2lambda's dev has moved since the lock (pinned at 6699c53; dev is now a76603d): t44 freezes converted documents unwrapped with display maths on its own lines, t48 takes a list of selectors per role and reports a doubled block instead of refusing, t50 adds draft field set FIELD --text RANGE (quote a range into a field already written) and t53 adds draft part solution PART --text RANGE.

Relock in2lambda at dev head in pyproject.toml/poetry.lock. Then give the fix loop the two new commands as tools in in2lambda_agent/fix.py: field_set (field, text) for a finding that a field is empty or quotes the wrong lines, and part_solution (part, text or literal) for a part whose solution is on the sheet under it; describe each in the system prompt beside the six commands there. field set has no literal. package.py's command wrapper needs no change if it is generic; check. Update the corpus-specs and any fixture spec that t48's list form or t44's freeze changes, and tests/test_fix.py for the two tools. Then run the replay sweep (in2lambda-agent corpus <corpus> PHYS40002 --replay) and the UCL_MechEng PDF sweep and put both CSVs in the PR description, with the before/after built counts. Done when the lock names dev head, the two tools are offered and tested, and the replay sweep builds at least as many documents as before the relock.

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Workbench ticket t26.