chore(core): fix build.rs + crate-doc drift left by the W7/W8 splits

- build.rs: drop the stale `rerun-if-changed=src/client.rs` (the file
  became client/ in W7; the path never fires).
- lib.rs: the crate doc's module list named 6 of ~19 modules — add the
  missing ones (config/error/stats/input/reject/reanchor/render_scale/
  audio/wol + the quic-gated control-plane group), without intra-doc
  links to feature-gated modules.
- quic/mod.rs: the module doc still described the deleted `msgs`
  module; list the actual post-split module set.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-core/build.rs

@@ -10,7 +10,6 @@ fn main() {
     println!("cargo:rerun-if-changed=src/abi.rs");
     println!("cargo:rerun-if-changed=src/config.rs");
     println!("cargo:rerun-if-changed=src/input.rs");
-    println!("cargo:rerun-if-changed=src/client.rs");
     println!("cargo:rerun-if-changed=src/error.rs");
     println!("cargo:rerun-if-changed=cbindgen.toml");