chore: bump version 0.8.3 → 0.9.0

dogfood-discovered routing additions (PR #147) land:
- .mts / .cts → MediaType::Code(typescript)
- .mdx → MediaType::Markdown

minor bump 사유: 사용자 도그푸딩 surface 확장 — 이전에 skip 되던 28+ 파일이
이제 색인됨. design §10.4 dogfooding-ready surface 확장 = minor trigger.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -31,7 +31,7 @@ edition       = "2024"
 rust-version  = "1.85"
 license       = "MIT OR Apache-2.0"
 repository    = "https://github.com/altair823/kebab"
-version       = "0.8.3"
+version       = "0.9.0"
 
 [workspace.dependencies]
 anyhow       = "1"