chore(cli): add migration-self-contained lintoko example rule

[Kamirus]

Enhanced migration chains stay maintainable when each file is self-contained — importing packages (mo:…), canisters (canister:…), etc., but not sibling .mo modules. This adds a copyable migration-self-contained lintoko example rule that flags relative module imports in migrations/, aligned with the Motoko compiler's Url.Relative classification (import paths without :).

Before: no example rule for local imports in migration files.

After: with [lint.extra] configured:

"migrations/**" = ["lint/migration-self-contained"]

$ mops lint
  × [ERROR]: migration-self-contained
   ╭─[migrations/20250101_000000_Init.mo:3:14]
 2 │ import Backend "canister:backend";
 3 │ import Types "../src/Types";
   ·              ───────┬──────
   ·                     ╰── Migration files must not import local modules (relative paths). Got: "../src/Types"

The rule uses #match? @path "^\"[^:]*\"$" so any new compiler URL scheme (with :) is allowed without updating the rule.

blob:file: imports are out of scope — the compiler classifies those as FileValue, not Relative.

Made with Cursor

[github-actions]

Cursor AI review

👍 APPROVE — looks safe to merge

Category	Assessment	Details
Summary	✅	Adds a migration-self-contained lintoko example rule under cli/tests/lint-extra-example-rules/, with a migration fixture, [lint.extra] wiring, and snapshot coverage in the existing example-rules test. No production CLI, backend, or docs changes.
Code Quality	✅	Follows the existing example-rule fixture pattern; the tree-sitter query is minimal and matches the stated Url.Relative heuristic (no : in import path).
Consistency	✅	Aligns with sibling rules in lint-extra-example-rules and extends the existing snapshot test rather than adding redundant coverage.
Security	✅	Test-only changes; no auth, signing, registry, or package-integrity paths touched.
Tests	✅	Snapshot update is targeted to the new rule output (3 violations on relative imports; mo: and canister: imports pass).
Maintainability	✅	Rule includes includes = ["**/migrations/**"] so it stays copyable as a standalone rule; changelog/docs/skills updates are not required for internal test fixtures.

Verdict

Decision: APPROVE
Risk: Very Low
Reason: This is a contained test-fixture addition with no user-facing CLI or runtime behavior changes. The lint rule logic and snapshot expectations are consistent with the PR’s intent and existing [lint.extra] test patterns.

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Generated for commit b042819