docs: document screenReaderSpeed accessibility setting (PR #33)

[Copilot]

PR #33 adds screenReaderSpeed (uint8_t) as a new accessibility setting — a PersistentStore key and OnScreenReaderSpeedChanged event handler — with no corresponding documentation update.

Changes

• PRODUCT.md — Added screen reader speed to Accessibility Features list and Accessibility-Focused Applications use case
• ARCHITECTURE.md — Added screenReaderSpeed (uint8_t) to accessibility settings inventory; bumped total managed settings count 18 → 19
• plugin/CHANGELOG.md — Added v2.4.0 entry for the new parameter

Known gaps (pending SME review)

• Valid range and default value for screenReaderSpeed are not defined in the PR changes to test doc agent #33 diff — Get/SetScreenReaderSpeed implementation is not yet present. API reference in docs/ should be extended once that lands.

Warning

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• https://api.github.com/graphql
  • Triggering command: `/usr/bin/gh gh pr create --repo rdkcentral/entservices-usersettings --base develop --head melhar098:copilot/doc-update-33-docs --title [DOCS] Documentation updates for PR changes to test doc agent #33 - screenReaderSpeed setting --body ## Documentation Updates

This PR contains documentation updates for #33

Files Updated

• PRODUCT.md: Added screen reader speed to Accessibility Features and Accessibility-Focused Applications use case scenario
• A (http block)

• Triggering command: /usr/bin/gh gh auth status (http block)

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