Move license header to contrib/claude

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

AGENTS.md

@@ -29,6 +29,7 @@ Detailed guides for specific subsystems live in `contrib/claude/`:
 - [`contrib/claude/relay.md`](contrib/claude/relay.md) — Relay cursor pagination (cursor format, keyset pagination, schema types)
 - [`contrib/claude/graphql.md`](contrib/claude/graphql.md) — Frontend Relay client (queries, fragments, mutations, pagination)
 - [`contrib/claude/commit.md`](contrib/claude/commit.md) — Commit message conventions
+- [`contrib/claude/license.md`](contrib/claude/license.md) — ISC license header for Go files
 
 ## API Surface Rules
 
@@ -110,26 +111,6 @@ svc, err := foo.NewService(ctx, db, logger, foo.Config{
 })
 ```
 
-### License header
-
-Every `.go` file starts with the ISC license header. Use the **current year** for new files. When editing an existing file whose header has a different year, update it to a range (e.g. `2025-2026`). Never overwrite the original year.
-
-```
-// Copyright (c) <YEAR> Probo Inc <hello@getprobo.com>.
-//
-// Permission to use, copy, modify, and/or distribute this software for any
-// purpose with or without fee is hereby granted, provided that the above
-// copyright notice and this permission notice appear in all copies.
-//
-// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
-// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
-// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
-// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
-// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
-// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
-// PERFORMANCE OF THIS SOFTWARE.
-```
-
 ### Import ordering
 
 Two groups separated by a blank line: stdlib, then everything else (third-party and internal sorted together alphabetically).