Bumps `@version` to 0.3.0, assembles the fourteen pending changelog
fragments into a `## [0.3.0]` section, and deletes them in the same
commit per changelog.d/README.md.

A minor rather than a patch: `StatifierUI.Live` and its read model,
`StatifierUI.Live.ExpressionInput` and `StatifierUI.Expression`,
`StatifierUI.Trace.Capture`, `Projection`, `Otel`, `DeepLink`, and
`Json.decode/1`, plus the inspector's scrubber API, are all new public
surface since 0.2.0. Nothing is removed and nothing breaks: `otel` and
`$redacted` are additive reservations, the wire format stays at
version 1, and `Inspector.event_log/1` keeps its behaviour beside the
new `event_log/2`.

Every fragment entry carries over byte for byte, grouped Added /
Changed / Fixed, including the closing prose paragraphs four fragments
wrote under their own headings.

Moves the README install pin from `~> 0.1` to `~> 0.3`. It had been
left behind at the 0.2.0 prep, so the recipe's `readme_pin` step
repairs the drift by moving straight to the new minor.

`assets/package.json`'s "version" is deliberately untouched: the
release extension records it as not a release carrier.

The tag, the GitHub release, and `mix hex.publish` are deliberately
not part of this commit.

Refs: sui-dba