The new edge-only hooks pages linked each other with versionless paths
like `/learn/step-hooks`, which mintlify resolves against the frozen
default version where those pages do not exist, breaking the CI link
check. Uses the `/en/learn/...` form the other edge pages already use.
The hooks pages sat flat in the learn nav and only documented the LLM
and tool call contexts, with examples built on the legacy decorators.
Groups them under a collapsible "Execution Hooks" section, adds
`step-hooks` and `execution-boundary-hooks` pages covering every hook
context from source, reworks the LLM and tool pages to lead with `@on`
while keeping the decorators, and links the orphaned
`before-and-after-kickoff-hooks` page into the group.
