Fix meta_engine genesis validator: cap solo_time_estimate at 16h not 24h

On line 152, change the condition from `p.solo_time_estimate > 24` to `p.solo_time_estimate > 16`. Update the error message on line 153 from '(1-24h)' to '(1-16h)'. This aligns validateProposal() with the META_PROPOSER_SYSTEM instruction on line 42 which states 'should be ≤16; reject if you'd estimate days/weeks'. No other changes. As a followup, query engine.db for `SELECT id, title FROM hypotheses WHERE lane='meta' AND json_extract(description, '$.solo_time_estimate') > 16` to identify any proposals that passed this check incorrectly.

Proposals with solo_time_estimate in the 17-24h range are now caught by validateProposal() and routed to rejected[] instead of persisting to the DB. The enforcement gap between the system prompt contract (16h) and the validator implementation (24h) is closed. Historical retrocheck: if any meta-lane proposal in engine.db has solo_time_estimate 17-24, it passed a check it should have failed.

Call validateProposal({ title: 't', change_type: 'TOOL', target_files: ['x.js'], proposed_diff: 'y', expected_effect: 'z', falsifier: 'f', solo_time_estimate: 20, reversibility: 'SIMPLE' }). Before fix: returns {ok: true}. After fix: must return {ok: false, reason: 'solo_time_estimate out of range (1-16h): 20'}. If the post-fix call still returns {ok: true}, the wrong comparison was edited.

Approved by Commander review. Queued for or completed implementation by Architect.