v0.2.3

chore(release): prepare binary 0.2.3

Binary-only cut (docs/RELEASING.md): `content/skills/**` is untouched since
v0.2.2, so no pack bump, no `pack_drift` bless and no `skills.ctxpkg-hash`
sync; `content/core|gloss|templates` are untouched too, so no seed bless.
`version_req = "^0.2"` still covers the published pack.

Version in `Cargo.toml` (+ lock) and `[addon]` of `lean-ctx-addon.toml`.
`[artifacts.*]` deliberately left on the v0.2.2 url/sha256 — the release
workflow's sync-manifest job patches both from SHA256SUMS after the tag build,
and hand-editing them is what shipped the 0.2.1 url/hash mismatch.

`min_lean_ctx` stays at 3.9.6 even though the anchors this release repairs need
lean-ctx >= 3.10.1 (`lean-ctx call` opens no session below that). Package B is
precisely the degradation path for an older lean-ctx, so raising the floor would
turn a working fallback into a hard preflight refusal for no functional gain.
The CHANGELOG states the 3.10.1 requirement instead.

Gates green at 0.2.3: 702 passed / 16 skipped, clippy --all-targets
--all-features -D warnings clean, fmt clean.