feat: surface OCR and translation failures with toasts

[Arimacose]

Summary

• show a deduplicated Toast when OCR or translation/model preparation fails, including timeout-specific wording
• show one Toast per no-valid-text episode in both region and full-screen capture modes
• preserve actionable Online error categories across shared service UI and Online settings, covering API Key, endpoint/model, HTTP, DNS, TLS, timeout, rate-limit, server, network, and response failures
• keep secrets out of rendered text and retain the existing redaction boundary

Behavior

• repeated identical service failures are throttled for 8 seconds
• a blank OCR state emits once, rearms after valid text appears, and emits again only for a later blank episode
• Online settings now Toasts model-list, save/configuration, and translation-test failures in addition to its persistent status text

Validation

• testLiteDebugUnitTest: 293 tests, 0 failures
• testFullDebugUnitTest: 289 tests, 0 failures
• testOnlineDebugUnitTest: 323 tests, 0 failures
• lintLiteRelease lintFullRelease lintOnlineRelease: 0 fatal, 0 error
• Lite/Full/Online debug and release APK assembly succeeded
• Online contributor APK assembly succeeded
• Lite/Full/Online release AAB bundles succeeded
• provider-admission verifier: 22 tests passed and canonical evidence verified
• fresh Online failure evidence: 9/9, fresh_kotlin_policy_execution

Acceptance boundary

No device install or signed-device interaction was performed in this change. Runtime acceptance should focus only on the three new Toast paths and absence of APP fatal/ANR.