feat: preserve glob imports in generated migrations

[oxura]

The symbol resolver cannot enumerate names introduced by a glob import, so model field types reached generated migrations without either a fully resolved path or the import that made the name visible. It also emitted a warning even though the generator can preserve the original scope another way.

The resolver now extracts top-level glob branches from ordinary and grouped use trees. It rewrites self and super prefixes to stable crate-relative paths, preserves attributes such as cfg, and leaves explicit imports on the existing symbol-resolution path. Models carry those imports into generated migrations; imports from multiple changed models are deduplicated before emission.

Verification:

• red/green regression for crate-relative and super glob imports
• generated migration compile regression using a model whose macro and field type come from a glob
• Cot Codegen suites: 59 passed
• Cot CLI library suite: 52 passed
• migration generator integration suite: 15 passed
• cargo +1.94.0 fmt --all -- --check
• Cot Codegen and CLI Clippy across all targets/features with warnings denied (unknown-lints allowed for the upstream toolchain compatibility issue)

Closes #69.