fix(service): use start-whisper-server.sh in whisper start fallback

[codesmax]

Summary

Installation of voicemode with local whisper enables auto-start by default. If disabled, it removes launchd/systemd service files, such that voicemode service start whisper executes fallback logic to invoke the whisper-server binary directly. This omits important config + flags set in the start-whisper-server.sh wrapper that's aligned with the voicemode service:

• --inference-path /v1/audio/transcriptions
• --convert
• --threads

Notably the missing --inference-path flag causes whisper-server to serve at the default /inference path. This results in a 404 when voicemode attempts STT via the expected OpenAI-compatible endpoint: STT failed for http://127.0.0.1:2022/v1 (whisper): File Not Found (/v1/audio/transcriptions).

Fix is to invoke the wrapper script when available, and fall back to direct binary execution but with necessary missing arguments.

Test Plan

• make test succeeds => 1013 passed, 60 skipped in 61.93s (0:01:01)
• (on fix branch) uv run voicemode service start whisper => verified wrapper execution with correct flags set; voicemode converse with local whisper works

Side note: thanks for building such a sweet tool! 🙏

[ai-cora]

Great bug fix — nice root cause analysis and clean minimal diff. The two-tier approach (prefer wrapper script, fall back to direct binary with correct flags) is exactly right.

Minor observations (non-blocking):

• config_vars is computed before the if service_name == "whisper" block so it also runs for kokoro/voicemode/connect fallback paths where it's unused. Could be scoped inside the whisper block, but harmless as-is.
• The direct binary fallback doesn't include --threads (the wrapper auto-detects via nproc/sysctl). Not a regression since the original didn't have it either, but worth noting for completeness.

Architectural note for us (not on you!): We spotted that this whole fallback path exists because uninstall_service() deletes the plist/systemd unit file rather than disabling it. Both launchd and systemd support disable-without-delete, which would let service start always route through the service manager → start script. We'll track that cleanup separately. Your fix is the right thing for now.

Thanks for the contribution and the kind words! 🙏

[codesmax]

Saw that the merge was blocked since the commit in my PR wasn't signed. Sorry about that. I just updated the branch with a signed commit (with no changes otherwise).