chore(release): prep v0.18.0

[mrdushidush]

Release prep only. Three files, matching the v0.17.0 prep exactly.

• crates/claudette/Cargo.toml + Cargo.lock -> 0.18.0
• CHANGELOG.md: roll [Unreleased] into ## [0.18.0] - 2026-09-05, add the [0.18.0] and updated [Unreleased] compare-link refs

No code changes. release.yml's tag-version-match job checks the tag against both Cargo.toml and Cargo.lock, so both are bumped here.

Why now

crates.io has served 0.17.0 since 2026-07-19. main is 47 commits ahead. Anyone running cargo install claudette today gets none of:

• the --offline $HTTP_PROXY leak fix (a loopback URL passed the host guard but the socket still went to the system proxy, carrying the conversation with it, banner on screen)
• three apply_diff bugs that corrupted files while reporting ok: true
• write_file overwriting an existing file with no prompt and no preview
• /undo silently doing nothing after apply_diff / apply_patch / edit_file
• a post-edit check that read its own 10s timeout as a pass
• the empty-turn cluster

Gate

Run on 1.98.1 (what CI's dtolnay/rust-toolchain@stable resolves to) at -j 2:

check	result
cargo fmt --all --check	pass
cargo clippy --all-targets --no-deps -- -D warnings	pass
cargo clippy --all-targets --all-features --no-deps -- -D warnings	pass
cargo test -p claudette --lib	1161 passed, 0 failed
cargo test -p claudette --lib --all-features	1248 passed, 0 failed
cargo test -p claudette --lib --bins	1161 + 32, 0 failed

That last shape is the one release.yml's verify job runs, so the tag's own gate is known green before the tag exists.

After merge

git tag -a v0.18.0 -m "..." && git push origin v0.18.0 fires crates.io (OIDC) + 5 prebuilt binaries + the GitHub Release. Worth a gh workflow run release.yml dry-run first - it runs verify + audit + deny + build-binaries and skips publish/release.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WBTQNHWbko1wpeBrcmL3de