`sqlmesh lint` should accept model file paths

[cmgoffena13]

Summary

sqlmesh lint can target models with --model NAME, but not with file paths. Pre-commit and other path-based tools pass filenames, so lint cannot be wired up without a wrapper that maps paths to names.

Current behavior

• sqlmesh lint --model sushi.orders works
• sqlmesh lint models/orders.sql is a Click extra-arg error
• sqlmesh lint --model models/orders.sql looks up a model with that name and fails
• --local and --use-project-index already exist and should keep working when the selection comes from paths.

Proposed CLI

sqlmesh lint --local --use-project-index models/a.sql models/b.py

• Add a positional paths argument (nargs=-1), same shape as sqlmesh format
• Resolve each path to the model(s) whose _path matches
• Keep --model for names; paths and --model can be combined
• No paths and no --model still lints every model
• With --use-project-index, path resolution should use the index (relative path -> FQNs) so unrelated models are not loaded

Acceptance

• Lint of one changed model file does not lint the rest of the project
• Python and SQL model files both work
• Unknown path fails with a clear error (does not lint everything)
• Existing --model usage is unchanged