refactor(runtime): simplify production code and converter views

[chamsechan]

Simplify production code by removing unused helpers and duplicated state/processing. Production C/C++ sources decrease from 27,995 to 27,585 physical lines (410 lines, 1.46%; excluding CLI, tests and third-party code).

• Represent each converter batch view as its declared single external slot, preserving type checks, optional row positions, trusted runtime bindings and output lease behavior. Reuse row decoding for image/question inputs.
• Remove unused adapter validation helpers, unused enum/constants, the unimplemented threshold control command and unreachable catches around noexcept calls. Remaining control command IDs stay 1, 2 and 4.
• Remove duplicated ranking state and checks; share template-token rendering and SelectBatch result handling while preserving provenance and callback precedence.

Validation: the canonical local gate passed with 394 tests passing and one GGUF-dependent test skipped because EDGEFLOW_TEST_LLAMA_GGUF was not provided. Seven existing CPU pipelines passed validation and plan generation. Focused regressions cover slot/type mismatches, trusted callback replacement, literal template insertions and SelectBatch callback precedence. Independent review found no defects.