chore(release): v1.8.1

[stephenleo]

Cuts v1.8.1, covering the three commits on main since v1.8.0.

• Bump Cargo.toml / Cargo.lock to 1.8.1
• Promote ## [Unreleased] → ## [1.8.1] - 2026-08-04
• Add the missing changelog entries for feat(config): publish JSON schema for editor autocomplete #197 (config JSON schema) and feat(model): add family_style map for new model families #195 (family_style map) — only feat: add $fill layout token (Starship-style right-alignment) #189's $fill entry was recorded

Merging does not publish; the release workflow fires on the v* tag, pushed after merge.

Verified: cargo fmt --check, cargo clippy --all-targets -D warnings, cargo test (591 passed).

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