Rename --model → --lm and --text-encoder → --embedding in ace-* CLI invocations

[Copilot]

Upstream acestep-cpp binaries changed two CLI parameter names that must be reflected in all ace-* tool invocations.

Changes

• server/src/services/acestep.ts
  • ace-lm call: --model → --lm
  • ace-dit call: --text-encoder → --embedding
  • ace-understand call: --model → --lm
• server/src/routes/generate.ts
  • ace-lm (lyrics-to-tags): --model → --lm

The --model flag in referenceTrack.ts (Whisper transcription) is unrelated and left unchanged.

// Before
['--request', requestPath, '--model', lmModel]
['--text-encoder', textEncoderModel, ...]

// After
['--request', requestPath, '--lm', lmModel]
['--embedding', textEncoderModel, ...]