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>

.cursor/rules/coredata-migrations.mdc

@@ -23,7 +23,7 @@ date -u +"%Y%m%dT%H%M%SZ.sql"
 
 ## License header
 
-Every `.sql` file starts with the ISC header (use the current year). Copy
+Every `.sql` file starts with the MIT header (use the current year). Copy
 the exact block from `contrib/claude/license.md` (SQL section).
 
 ## Content rules