Add implementation plan for integrating useSpeech (react-text-to-speech)

[carloshskp]

Motivation

• Document the migration to the useSpeech API from react-text-to-speech to replace or encapsulate the current window.speechSynthesis flow while preserving UX, accessibility and i18n.
• Establish a mandatory quality gate requiring >= 95% unit test coverage for impacted modules before swapping engines to avoid regressions.
• Provide a clear, incremental strategy and acceptance criteria to enable a safe rollout with fallbacks and observability.

Description

• Added docs/useSpeech-implementation-plan.md containing the full migration plan, scope, out-of-scope items, and a phased execution strategy.
• Defined a speech engine abstraction with the SpeechEngine contract and adapters RttsSpeechEngine and NativeSpeechEngine to decouple UI from engine implementation.
• Specified integration points such as src/app/textReaderApp.ts, state mappings for speechStatus, handling of rate and i18n, error/observability hooks, and fallback behavior.
• Included a comprehensive testing plan, required unit test scenarios, CI coverage gate (>= 95%), documentation updates (README.md, README.pt-BR.md), and definition of done.

Testing

• This change is documentation-only and no automated tests were executed as part of this PR.

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Codex Task