Add the MIT license (closes #14)

Adds LICENSE with the standard MIT text and "Copyright (c) 2026 sneak", the license sneak chose. The README now calls keyfunc MIT-licensed in its first paragraph, its License section points at LICENSE, and the license line leaves the TODO list.

Model: opus-5-5

README.md

@@ -1,11 +1,10 @@
 # keyfunc
 
-`keyfunc` is a Go command-line tool by [@sneak](https://sneak.berlin) — its
-license is not yet chosen
-([#14](https://git.eeqj.de/sneak/keyfunc/issues/14)) — that turns a BIP-39
-mnemonic into SSH keys, age identities and child mnemonics, each of which can be
-recreated from that mnemonic at any time. The same mnemonic, key type and index
-always give the same key.
+`keyfunc` is an MIT-licensed Go command-line tool by
+[@sneak](https://sneak.berlin) that turns a BIP-39 mnemonic into SSH keys, age
+identities and child mnemonics, each of which can be recreated from that
+mnemonic at any time. The same mnemonic, key type and index always give the same
+key.
 
 It uses the BIP-85 entropy deriver from `git.eeqj.de/sneak/secret/pkg/bip85` and
 takes the same steps as that repository's `agehd` package.
@@ -306,14 +305,11 @@ standard: most Makefile targets are thin shims over an executable in
 
 The open issues that stand between the tree and a 1.0 release:
 
-- [#14 Choose a license and add LICENSE](https://git.eeqj.de/sneak/keyfunc/issues/14)
 - [#15 Decide the Go module path before 1.0](https://git.eeqj.de/sneak/keyfunc/issues/15)
 
 ## License
 
-Not yet chosen. The license is the owner's decision, still open on the tracker
-([#14](https://git.eeqj.de/sneak/keyfunc/issues/14)); the `LICENSE` file is added
-when that issue is answered.
+MIT. The full text is in [`LICENSE`](LICENSE).
 
 ## Author