Add shared form controls for settings

[raiseCatError]

Implements #167.

Stacked on #217 (feature/166-actions), which is stacked on #203. Merge order: #203, #217, then this PR; retarget each to dev after its base merges.

What changed

• src/ui/formControls.ts: toggle, select, multi-select, text field and confirmation. Key handlers return the proposed value (or nothing) and never store or write it; the owning feature persists.
• Rendering has a plain path with no escape sequences. Focus is a > marker, changed state is (changed) and errors are Error: ... text, so none of them depend on color.
• renderField composes label, control, description, changed state and error, and truncates to narrow widths.

Consumers

• Settings boolean and enum rows step through the shared toggle and select behavior.
• The Settings search box edits through editText. This also makes paste and delete-word work in the search box.
• Multi-select and confirmation have no consumer yet; Settings experience v2: searchable registry and progressive disclosure #169 is expected to use them (reset-current-setting confirmation, module lists). They are small and tested here.

Verification

tests/formControls.test.ts covers proposals, keyboard-only use, plain rendering and narrow widths. Full suite 632/632, typecheck, build and git diff --check clean.