fix: add controller helper parity accessors

[rlippmann]

Summary

• sync the current Python public API fixture contract into the TS repo
• add controller helper parity accessors and snake_case aliases
• refresh controller, integration, and README wording to prefer helper-first and host-flow framing
• bump the package release to 0.7.4

Why

This branch brings the TypeScript package into parity with the current Python controller helper surface, updates docs/examples to reflect the current project framing, and includes the corresponding package release bump.

Scope checklist

• Diff is minimal and scoped to the requested behavior
• Python/spec parity is preserved (or mismatch is explicitly documented)
• Fixture semantics are respected (exact string vs non-empty null rule)
• No unrelated refactors
• Relevant validation was run (npm test for behavior changes, or docs-only/no-runtime-change)

Notes

Validation details:

• npm test: passed
• If not run, why: n/a