fix(workflows): resolve manifest service aliases in workflow dependency checks

[0xacee]

Summary

POST /api/workflows/{id}/enable (and the workflow list availability flags) can never succeed for the shipped voice-to-voice workflow.

• The catalog (config/n8n/catalog.json) declares its dependencies as ["whisper", "llama-server", "kokoro"].
• The Kokoro service's manifest id is tts; kokoro is only a declared alias (extensions/services/tts/manifest.yaml → aliases: [kokoro]).
• check_workflow_dependencies resolved deps against SERVICES keys plus a single hardcoded legacy alias (ollama → llama-server). kokoro resolved to nothing → results["kokoro"] = False → enable responds 400 Missing dependencies: kokoro even while TTS runs healthy, and the workflow list marks it permanently unavailable.

Why this matters

Enabling voice-to-voice fails 100% of the time on a correct install, with an error message blaming a "missing" service that is actually running. Manifests have declared aliases for a while (kokoro, llm, workflows, webui, agent, …); any future workflow or feature check written against those names hits the same trap.

Fix

• config.py: expose the manifest's aliases list on each SERVICES entry (additive field).
• routers/workflows.py: _service_aliases() builds the alias→id map from SERVICES, and check_workflow_dependencies resolves each dep through the legacy map first, then manifest aliases. Unknown deps still return False unchanged.

Tests

• test_check_workflow_dependencies_manifest_alias: SERVICES["tts"] = {aliases: ["kokoro"]} + healthy mock → result["kokoro"] is True, and the health probe is called with the resolved id tts. Fails on public-beta base (result["kokoro"] is False), passes here.
• test_check_workflow_dependencies_manifest_alias_unhealthy: same alias with a down service → False (no false-positive availability).
• Full tests/test_workflows.py: 49/49 pass; py_compile + git diff --check clean.

Overlap check

Searched open PRs touching routers/workflows.py, config.py, tests/test_workflows.py: #5644 (activation-failure reporting inside enable_workflow), #5672 (malformed catalog/executions tolerance), #5829/#5828 (inventory traversal, export), #5554 (exact-name matching), plus mechanical idioms PRs (#5485, #5567, #5571, #5575). This change is confined to check_workflow_dependencies and one additive service_config field — disjoint from all of them.