[codex] Fix PocketTTS language initialization

[mimeding]

Summary

• pass FluidAudio PocketTTS language into model download initialization
• align PocketTTS cache detection with the v2/english language-pack directory
• keep manager initialization explicit about the selected language

Why

The TTS branch no longer compiles against the current FluidAudio API because PocketTtsResourceDownloader.ensureModels now requires a language argument.

Verification

• swiftlint --strict Packages/OsaurusCore/Managers/TTSService.swift
• swift test --filter ChatViewSandboxTests/prepareChatExecutionMode_usesSessionAgentInsteadOfActiveAgent

[mimeding]

Follow-up from the live debug pass: the FluidAudio/PocketTTS compatibility fix verifies locally against the TTS branch.

Local checks:

• swiftlint --strict Packages/OsaurusCore/Managers/TTSService.swift passed.
• swift test --filter ChatViewSandboxTests/prepareChatExecutionMode_usesSessionAgentInsteadOfActiveAgent passed after compiling the branch.

GitHub test-core is currently failing before tests execute with the same EventSource module-resolution issue (CAsyncHTTPClient, CNIOLLHTTP, CNIOExtrasZlib, CNIOPosix, _NumericsShims). That is the shared CI failure addressed by #975, not a new TTS failure. Recommended order: land #975, rerun #977, then use this as the narrow unblocker for #962.

[mimeding]

Status update after adding the clean-PR rule: this companion PR is now draft because its attached GitHub checks are not clean yet. It should move back to ready only after the shared CI fix in #975 lands/rebases into the branch and scripts/ci/check-pr-clean.sh osaurus-ai/osaurus 977 passes.