Move the Go module to sneak.berlin/go/keyfunc (closes #15)

REPO_POLICIES.md sets the Go module root to sneak.berlin/go/<name>.
go.mod, every import of the old path and the -X path in the Makefile
LDFLAGS now use sneak.berlin/go/keyfunc; make fmt moved those imports
to their new place in the sort order. The old path keeps no alias. The
README gives the go install line next to the build from a clone and
drops this issue from its TODO list, which now names the open 1.0
issues.

Model: opus-5-5

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 sneak
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

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.
@@ -312,13 +311,14 @@ 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)
+- [#38 Lint and test as phases of the Dockerfile, as the current repo policy requires](https://git.eeqj.de/sneak/keyfunc/issues/38)
+- [#39 make fmt and make fmt-check cover Markdown with prettier](https://git.eeqj.de/sneak/keyfunc/issues/39)
+- [#40 The linter config, .gitignore and .dockerignore from the current templates](https://git.eeqj.de/sneak/keyfunc/issues/40)
+- [#42 go-bip39 no longer exists upstream: keep it, or copy it into the repo?](https://git.eeqj.de/sneak/keyfunc/issues/42)
 
 ## 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