feat(A.1 #6): fail Windows build when tokenizers enters the dep graph

Adds a build.rs guard that parses Cargo.lock and panics on Windows
if the tokenizers crate ever appears in the workspace dependency
tree, mirroring the MSVC C-runtime conflict that broke Whispering
v7.11.0 when they linked whisper-rs-sys + tokenizers in the same
binary.

On non-Windows hosts the guard downgrades to a cargo:warning so
cross-compilation or CI from Linux surfaces the issue before a
Windows build attempt actually panics.

No tokenizers crate is in the tree today; the guard is preemptive.
If we ever legitimately need HF tokenizers on Windows, the escape
hatch is an out-of-process sidecar (separate CRT).

Co-authored-by: jars <jakejars@users.noreply.github.com>

crates/transcription/Cargo.toml

@@ -3,6 +3,7 @@ name = "kon-transcription"
 version = "0.1.0"
 edition = "2021"
 description = "Speech-to-text engine wrappers, model management, and inference concurrency for Kon"
+build = "build.rs"
 
 [dependencies]
 kon-core = { path = "../core" }