fix(announcer): swallow benign speech interruptions

[chiefcll]

What

Error: Speech synthesis error: interrupted was spamming the console during directional navigation. This makes the announcer correctly treat speech interrupted/canceled as the benign, expected events they are.

Why

The error originates in speak()'s utterance.onerror (speech.ts). interrupted/canceled fire on every normal announcement, because each new announcement calls synth.cancel() to replace the in-flight one.

speakSeries already intended to swallow these, but the swallow branch was gated on e instanceof SpeechSynthesisErrorEvent — while speak() rejected a plain Error. So:

• the instanceof check was always false → the error hit else { throw e },
• which rejected the series promise,
• which, on the non-notification announce path (never .catched), surfaced as an unhandled rejection in the console.

The same dead branch also defeated the network retry logic, and SpeechSynthesisErrorEvent isn't defined as a global on every TV browser (a ReferenceError waiting to happen if the branch ever evaluated).

Changes

• speak() now rejects an Error that carries the structured .error code.
• Added a single handleSpeechError() classifier (replacing two copy-pasted catch blocks) that classifies by the .error code string:
  • interrupted/canceled → stop retrying silently (no longer surfaced),
  • network → back off and retry (this path was also dead before),
  • anything unexpected → rethrow.
• Dropped the dependency on the SpeechSynthesisErrorEvent global.

Reviewer notes

• A genuinely unexpected speech error (e.g. synthesis-failed) on the non-notification path still has no .catch in announcer.ts, so it would be an unhandled rejection. That's now rare and arguably should be visible — happy to add a .catch safety net on the returned series if preferred.

Verification

• npm run tsc — clean
• npm run lint — 0 errors (speech.ts introduces no new warnings)
• npm run test — 124/124 pass

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