[alcides]

External library specifications were previously rejected as unsupported. This change lets application code refine JDK and third-party library methods, constructors and fields through @ExternalRefinementsFor, using the same contracts in Latte and LiquidTypeChecking. For example, an ArrayList transition through a local alias is visible when checking the original variable's size.

• Resolve and validate Java signatures, overloads, inherited members and field types in a per-model registry stored on Spoon's AST. Placeholder bodies and field initializers do not become implementation facts.
• Apply ownership contracts to external parameters and results, including constructor parameters. Preserve shared-object rejection, borrowed mutation effects and consumption of all caller aliases on @Free transfers.
• Check parameter/result refinements, state transitions and state sets. Include external calls and constructor effects in loop analysis, and retain conservative global and unknown-call effects.
• Add CLI/API classpath support and analyze separate specification/application paths together. A test builds a library JAR and verifies both API and CLI use without initializing the library.
• Add checked examples, an external-specification guide, 42 focused tests and 15 promoted upstream inputs. All 410 imported fixture sources remain unchanged.

Validation: mvn -B spotless:apply clean verify -Pcompatibility passes with 522 tests, zero failures/errors, and 180/311 exact upstream matches (previously 165), with zero analysis crashes. The compatibility gate still checks every imported input and rejects newly accepted negative cases.

Library specifications are trusted contracts. Container-size specifications do not infer element ownership or return aliases. Expanded varargs calls require explicit arrays; varargs method references require an explicit-array lambda. These boundaries are documented and unsupported adapters are diagnosed explicitly.

This PR is stacked on feat/latte-liquid-typechecking, whose completed implementation was pushed as 1eb2448. Its diff contains only external-library support and related integration fixes. CI also runs for PRs targeting that base.