Bumps the version to 0.6.0 and assembles the single changelog.d
fragment into a dated 0.6.0 section, deleting it in the same commit,
and moves the README's install pin to `~> 0.6` - the checklist in
changelog.d/README.md names all three as one step.

Minor rather than patch: the one fragment (sp-t01) is an `### Added`
entry - durable runs now emit statifier's own session telemetry - and
on 0.x this repo has cut a minor for every Added-only section, 0.4.0
and 0.5.0 included.

CLAUDE.md's "released (0.5.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-38d