Make license declarations consistently MIT

The source headers, LICENSE files, and license metadata had drifted
apart. Align the entire project to MIT:

- Convert every source-file header to the MIT text across all comment
  styles (Go, TS, TSX, JS, MJS, SQL, CSS, GraphQL, shell), including
  SPDX-License-Identifier tags
- Set the root and cookie-banner LICENSE files to the MIT text with a
  "MIT License" title line
- Switch the package.json license fields, Docker image label, and
  cookie-banner README to MIT
- Update docs and the genmodels header generator accordingly
- Normalize copyright lines to a single format
  (Copyright (c) <year(s)> Probo Inc <hello@probo.com>.): unify the
  hello@getprobo.com and hello@probo.inc emails to hello@probo.com and
  the comma-separated years to a hyphenated range

Genuine third-party references are intentionally left untouched: the
Lucide icon attributions (Lucide is ISC) and the trivy dependency
license allowlist.

Signed-off-by: Sacha Al Himdani <sacha@probo.com>

packages/prosemirror/src/hasMarkdown.ts

@@ -1,5 +1,5 @@
 // Copyright (c) 2026 Probo Inc <hello@probo.com>.
-// Use of this source code is governed by the ISC license
+// Use of this source code is governed by the MIT license
 // that can be found in the LICENSE file.
 
 function isTableSeparatorCell(cell: string): boolean {

packages/prosemirror/src/htmlBlock.ts

@@ -1,5 +1,5 @@
 // Copyright (c) 2026 Probo Inc <hello@probo.com>.
-// Use of this source code is governed by the ISC license
+// Use of this source code is governed by the MIT license
 // that can be found in the LICENSE file.
 
 import DOMPurify from "dompurify";

packages/prosemirror/src/index.ts

@@ -1,5 +1,5 @@
 // Copyright (c) 2026 Probo Inc <hello@probo.com>.
-// Use of this source code is governed by the ISC license
+// Use of this source code is governed by the MIT license
 // that can be found in the LICENSE file.
 
 export { hasMarkdown } from "./hasMarkdown";

packages/prosemirror/src/markdown.ts

@@ -1,5 +1,5 @@
 // Copyright (c) 2026 Probo Inc <hello@probo.com>.
-// Use of this source code is governed by the ISC license
+// Use of this source code is governed by the MIT license
 // that can be found in the LICENSE file.
 
 import { lexer, type Token, type Tokens } from "marked";