refactor(rules): split angular.md into index + references

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

shared/rules/angular/references/components-and-state.md

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+## Components
+
+* Use `ChangeDetectionStrategy.OnPush` unless there is a concrete reason not to.
+* Prefer signal-based state for local component state.
+* Prefer `computed` for derived state.
+* Prefer `effect` only for actual side effects.
+* Do not use `effect` as a replacement for normal data flow.
+* Keep component state minimal.
+* Avoid duplicating derived state.
+* Prefer immutable state updates.
+* Avoid direct mutation of shared state.
+* Keep inputs and outputs strongly typed.
+* Prefer signal-based inputs and outputs when consistent with the project.
+* Avoid unnecessary two-way binding.
+* Avoid unnecessary component-to-component coupling.
+* Prefer explicit data flow from parent to child and explicit events upward.
+* Do not expose internal component state unnecessarily.
+* Use lifecycle hooks only when required.
+* Avoid complex initialization logic inside constructors.
+
+## Signals and State
+
+* Prefer signals for local and synchronous reactive state.
+* Prefer `computed` for derived values.
+* Keep signals private when external mutation is not intended.
+* Expose readonly state where practical.
+* Avoid storing values that can be derived from existing state.
+* Avoid circular signal dependencies.
+* Avoid side effects inside `computed`.
+* Keep effects small and deterministic.
+* Clean up resources created by effects.
+* Do not use global state unless multiple unrelated parts of the application genuinely need it.
+* Do not introduce a state-management library without a clear requirement.