Bumps the version to 0.5.0 and assembles the two changelog.d fragments
into a dated 0.5.0 section, deleting them in the same commit, and moves
the README's install pin to `~> 0.5` - the checklist in
changelog.d/README.md names all three as one step.

The section is Added-only: the dispatch context's `:invoke` field
(sp-2yx) and the ADR-0009 telemetry surface (sp-m0i). The other three
026 beads in this lane touched only ADRs, CI comments, and CLAUDE.md,
so they correctly left no fragment.

CLAUDE.md's "released (0.4.x on Hex)" line is left alone: it states
what is published, which stays true until the operator publishes.

No tag and no publish: those stay with the operator.

Refs: sp-3be