Scala SDK: add agent reflection and dynamic invocation

[noise64]

• resolves GOL-52
• adds Scala discovery, graph-backed schema/JSON conversion, reflected clients, caller-codec definitions, and direct invocation
• uses component-free environment-scoped ParsedAgentId; implementing component identity remains deployment metadata on AgentType
• keeps Scala caller-codec definitions as complete contracts whose type name is paired with a constructor codec and client factory; inherited binding-only Rust/TypeScript contracts derive their target from ParsedAgentId
• inherits direct WIT string reflection host identities without a generated host AgentId alias
• shares immutable decoded schema graphs, validates required outputs, and rejects unsupported non-awaited streams
• updates the common and Scala reflection skills and generated guide
• restacked on Rust SDK: add agent reflection and dynamic invocation #3811 with a merge commit; remains a draft

Verification

• Scala core tests: 636 passed
• sbt scalafmtCheckAll
• all three Scala guest runtimes regenerated
• ordinary export contract and role-matrix contracts passed; tracked declarations are clean
• inherited validation includes WIT drift, golem-common, Rust caller-contract UI/unit checks, TypeScript build/typecheck/tests/lint/template rebuild, and focused reflected RPC coverage
• fresh CI for head 7e6b1f8c4 pending

[github-actions]

📖 Docs preview: https://docs-au565o3xz-golem-cloud.vercel.app

Built from commit 7e6b1f8c45f5eeb2fdef860d46629d20cf23da61 by docs.yaml.

[noise64]

Superseded by #3875, which is based directly on main.