release: prepare 0.52.0

[justinjoy]

Summary

Release-preparation PR for wirelog 0.52.0, following docs/RELEASE_PROCESS.md §2.

• Bumps project_version in meson.build 0.51.99 -> 0.52.0.
• Moves the [Unreleased] changes under ## [0.52.0] - 2026-06-28 in CHANGELOG.md and resets [Unreleased] to the placeholder shape.
• Adds the 0.51 -> 0.52 entry to docs/MIGRATION.md and refreshes Last Updated.

Changes included since v0.51.0

Fixed

• Unsafe variables in negated body atoms (Parser accepts unsafe variables in negated body atoms #920): IR lowering now rejects rules where a named variable appears only inside a negated body atom (e.g. c(X) :- a(X), !b(X, Y).). Wildcards and constant columns remain accepted.
• String literal escape decoding ([codex] fix string literal escapes #925): the lexer now recognizes \" and \\ escapes inside string literals.

Documentation

• Negation and side compounds (docs(compound): guide users to negation workaround for side compounds #921): documents the positive-extraction workaround for negating side-tier compound body patterns; the IR-conversion error now names it.

Excluded as internal-only: sccache CI caching, post-0.51 dev version bump.

Verification

• scripts/ci/check-changelog-format.py -> OK
• scripts/release/extract-changelog-section.sh 0.52.0 produces the expected section
• No code changes in this PR; the feature commits (Parser accepts unsafe variables in negated body atoms #920/[codex] fix string literal escapes #925/docs(compound): guide users to negation workaround for side compounds #921) already merged and passed CI on main.

Next steps (post-merge, per RELEASE_PROCESS.md)

• Tag on main: git tag -s v0.52.0 -m "wirelog 0.52.0" && push
• gh release create v0.52.0 --notes-file <(./scripts/release/extract-changelog-section.sh 0.52.0)