feat: add create-signalstore skill (#108)

* feat: add create-signalstore skill (closes #107)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: remove repo-specific workflow from create-signalstore skill

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: expand create-signalstore skill with store-type prompts, rxResource, entity API

- Ask upfront: store type, external data needs, singleton vs scoped
- Add dedicated rxResource section as preferred data-loading pattern
- Show rxMethod for mutations alongside rxResource
- Add appRef.whenStable() testing pattern for rxResource
- Add withLinkedState for derived writable state
- Expand entity updater reference (full set: add/set/update/upsert/remove)
- Add named collections and custom ID selector (entityConfig)
- Cover rxMethod signal-input reactive tracking
- Fix withReducer example

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* docs: add component conventions to AGENTS.md

- .ts-only components: inline template, no .html/.css files
- No 'Component' suffix in file or class names
- ChangeDetectionStrategy.OnPush on all components
- data-testid on host via host property
- Use @testing-library/angular render/screen in component specs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: chrisjwalk-bot