feat(inference)!: replace managed routes with providers

[varshaprasad96]

Summary

Remove the managed inference-route stack now that provider v2 supplies native provider endpoints, and fold the next service/settings CLI module extraction into the same clean replacement branch. This keeps the #2304 refactor aligned with the architecture established by #3172.

Related Issue

Closes #3172
Relates to #2304
Supersedes #3188

Changes

• Remove the managed inference CLI, gRPC API, router crate, supervisor interception path, SDK clients, generated bindings, and obsolete examples/tests.
• Add SQLite and PostgreSQL migrations that remove legacy inference-route objects while preserving all other stored objects.
• Keep inference access provider-native, including provider type normalization and custom endpoint-bearing profiles, and document the upgrade path.
• Extract service and settings command implementations from the CLI run module into dedicated command modules.
• Update architecture, published docs, man pages, agent skills, Go/Python SDK surfaces, and repository metadata.

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (obsolete managed-route cases removed; provider endpoint coverage retained)
• mise run ci passes on the rebased branch
• mise run go:ci passes
• Focused Python SDK and wheel tests pass (137 tests)
• mise run e2e could not complete locally because the Docker daemon is unavailable

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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