maxlength was hard-coded to 200 in the markup while MAX_MODEL_CHARS lives
in lib/defaults.js; lowering the constant would have left the input
accepting values mergeSettings() silently discards. It is now set from the
constant at render time.
Also records the hasFocus() gate's four manual frame cases in AGENTS.md,
including the findbar trade-off, and notes that fitToBudget()'s budget
guarantee assumes mergeSettings-validated input.
golem