feat(ai): rank capability discovery by operation shape - #32

Summary

• rank capability discovery by compiler-owned operation shape before entity, execution target, namespace, and lexical relevance
• expose conservative compiler-owned result-record cost bounds through fixed-broker descriptions
• advance the capability-index contract and affected crate versions, with migration and reference documentation

Documentation impact

• Documentation updated
• No documentation impact

Validation

• tool-profile tests: 31 passed, including mixed-shape retention, narrow intent vocabulary, lexical-zero exclusion, and deterministic 505-entry ranking
• full AI provider-feature test matrix: 402 core tests plus all integration suites passed; 38 doctests intentionally ignored
• SQLite, PostgreSQL, MSSQL, and PascalCase feature checks passed
• Rustdoc passed with warnings and missing documentation denied
• documentation validation, release policy, formatting, and diff checks passed
• affected clippy matrix passed with the existing subscription_waits.rs large_enum_variant baseline lint explicitly allowed; no changed file introduces a warning

No database, data, GraphQL SDL, protected-payload, backup, or restore migration is required.