fix(settings): repair keep-warm minutes input UX

[quiet-node]

Summary

• Fix inability to clear a single-digit value and retype: add rawMin string state that allows empty intermediate values while inactivityMin (the debounced-save driver) stays numeric
• Fix out-of-bounds values not reflecting in the UI: clamp rawMin immediately on onChange so the display always matches what is saved
• Fix empty-field blur defaulting to previous value instead of 0: onBlur now resolves empty input to 0
• Fix input width clipping 3+ digit values: 32px → 48px
• Fix resync clobbering in-progress edits: minFocusedRef guards setRawMin in the resync block so a mid-debounce onSaved callback cannot reset the field while the user is typing

Test plan

• Type a value and verify config.toml auto-saves within ~250ms
• Clear all digits; input goes empty; blur → shows 0 and saves 0
• Type a value over 1440 (e.g. 9999); input immediately clamps to 1440
• Type a value below -1 (e.g. -99); input immediately clamps to -1
• Delete digits quickly; no ghost digit reappears mid-edit
• bun run test:all:coverage passes