refactor(rules): split ui-ux.md into index + references

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

shared/rules/ui-ux/references/content-and-feedback.md

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+## Content and Language
+
+* Use plain, concise language.
+* Prefer user terminology over internal technical terminology.
+* Avoid jargon unless the target users are expected to understand it.
+* Use consistent naming for the same concepts.
+* Do not rename concepts between screens.
+* Keep button labels, headings and descriptions concise.
+* Put the most important information first.
+* Avoid unnecessary explanatory text.
+* Add explanation only where users may reasonably be confused.
+* Error messages should explain what happened and what the user can do next.
+* Avoid blaming the user.
+* Avoid exposing stack traces, exception names or internal implementation details.
+
+## Feedback and System State
+
+* Always communicate important system state.
+* Show loading states for operations that are not immediate.
+* Avoid indefinite loading indicators without context.
+* Use progress indicators for longer operations where progress can be measured.
+* Clearly distinguish loading, empty, error and success states.
+* Do not leave blank screens where an empty state is expected.
+* Empty states should explain what the user can do next.
+* Show success feedback when the result is not otherwise obvious.
+* Keep transient notifications concise.
+* Do not hide important errors in temporary notifications.
+* Preserve actionable errors until the user has had a chance to understand them.
+* Do not silently fail.
+* Do not silently discard user input.
+
+## Responsiveness
+
+* The interface should feel responsive at all times.
+* Provide immediate feedback after interaction.
+* Avoid blocking the entire interface when only one section is loading.
+* Prefer localized loading states.
+* Use optimistic UI only when failures can be handled safely.
+* Avoid layout jumps during loading.
+* Reserve space for content where practical.
+* Keep animations short and functional.
+* Do not use animations that delay task completion.
+* Respect reduced-motion preferences.
+* Avoid unnecessary transitions and visual effects.