Improve missing preset project errors

[SiluPanda]

Summary

• disambiguate a missing registry route from a missing project after a preset request returns 404
• report Project '…' does not exist for nonexistent projects while preserving the existing unsupported-registry error for servers whose project still resolves
• cover the missing-project path without changing the existing 404/405 compatibility behavior

Verification

• uv run pytest src/tests/_internal/cli/services/presets/test_registry.py -q — 47 passed
• uv run pre-commit run --files src/dstack/_internal/cli/services/presets/registry.py src/tests/_internal/cli/services/presets/test_registry.py
• git diff --check

AI assistance

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Fixes #4222