drop the parity harness, keep what it argued

The harness compared these tools against the code they replaced — Python
imported from book-pipeline, podcast-pipeline and knowledge-mcp, and
JavaScript copied out of the podcast media server and indexer, each pinned to
a commit. All of it has since been deleted, so the live half cannot run and
the golden half pins answers against a source nobody can consult.

What was worth keeping was never the comparison. `KNOWN.md` argued, at
length, why a dozen of these tools deliberately do something a reader would
not expect: why pdfgutter measures the crop box throughout, why avplan finds
the encoder rather than reading one out of the environment, why mdscrub will
not manufacture a page boundary. Those arguments are about this code and
stand on their own, so they are now `docs/decisions.md`, rewritten to say
what each tool does and why rather than what it does differently.

Binding coverage is unaffected: the bindings carry 24 tests of their own, a
node smoke test against the built package, and a typecheck.

Cargo.lock

@@ -1095,28 +1095,6 @@ version = "1.70.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
 
-[[package]]
-name = "parity"
-version = "0.1.0"
-dependencies = [
- "avplan",
- "bibclean",
- "booksniff",
- "chunkmd",
- "corpus-core",
- "cuekit",
- "cuepack",
- "cueseg",
- "mdscrub",
- "mdsplit",
- "pdfgutter",
- "pdftriage",
- "rrf",
- "serde_json",
- "seriesof",
- "textkit",
-]
-
 [[package]]
 name = "pdfgutter"
 version = "0.1.0"