fix(models): deduplicate project sorting values and add unique constraints (#11334)

Project columns and cards use a sorting field for ordering, but nothing prevents duplicate values from being inserted. This causes unpredictable ordering and makes swap-based reordering unsafe. Additionally, the same issue can be added to a project multiple times, which shouldn't be possible.

This PR adds a migration to clean up existing data and enforce three unique constraints:
- (project_id, sorting) on project_board — one sorting value per column per project
- (project_id, issue_id) on project_issue — one card per issue per project
- (project_board_id, sorting) on project_issue — one sorting value per card per column

The migration deduplicates existing rows and reassigns sequential sorting values before adding the constraints.

Changes

- Migration: fix duplicate sorting values in project_board and project_issue, remove duplicate (project_id, issue_id) rows, add three unique constraints
- MoveColumnsOnProject: two-phase swap (negate then set) to avoid constraint collisions
- MoveIssuesOnProjectColumn: three-phase approach with duplicate validation and sorted lock ordering
- UpdateColumn: always persist sorting field (allows setting to 0)
- GetDefaultColumn: query max sorting before auto-creating
- createDefaultColumnsForProject: explicit sequential sorting
- changeProjectStatus: only set ClosedDateUnix when closing

## Checklist

The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).

### Tests

- I added test coverage for Go changes...
  - [x] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I added test coverage for JavaScript changes...
  - [ ] in `web_src/js/*.test.js` if it can be unit tested.
  - [ ] in `tests/e2e/*.test.e2e.js` if it requires interactions with a live Forgejo server (see also the [developer guide for JavaScript testing](https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/e2e/README.md#end-to-end-tests)).

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.

*The decision if the pull request will be shown in the release notes is up to the mergers / release team.*

The content of the `release-notes/<pull request number>.md` file will serve as the basis for the release notes. If the file does not exist, the title of the pull request will be used instead.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11334
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: Myers Carpenter <myers@maski.org>
Co-committed-by: Myers Carpenter <myers@maski.org>

models/fixtures/PrivateIssueProjects/project_board.yml

@@ -4,6 +4,7 @@
   title: Triage
   creator_id: 2
   default: true
+  sorting: 0
   created_unix: 1738000000
   updated_unix: 1738000000
 
@@ -13,5 +14,6 @@
   title: Triage
   creator_id: 2
   default: true
+  sorting: 0
   created_unix: 1738000000
   updated_unix: 1738000000

models/fixtures/PrivateIssueProjects/project_issue.yml

@@ -3,21 +3,25 @@
   issue_id: 6
   project_id: 1001
   project_board_id: 1001
+  sorting: 1
 
 -
   id: 1002
   issue_id: 7
   project_id: 1002
   project_board_id: 1002
+  sorting: 0
 
 -
   id: 1003
   issue_id: 16
   project_id: 1001
   project_board_id: 1001
+  sorting: 0
 
 -
   id: 1004
   issue_id: 1
   project_id: 1002
   project_board_id: 1002
+  sorting: 1

models/fixtures/TestPrivateRepoProjects/project_board.yml

@@ -4,5 +4,6 @@
   title: Triage
   creator_id: 2
   default: true
+  sorting: 0
   created_unix: 1738000000
   updated_unix: 1738000000

models/fixtures/TestPrivateRepoProjects/project_issue.yml

@@ -3,9 +3,11 @@
   issue_id: 6
   project_id: 1001
   project_board_id: 1001
+  sorting: 1
 
 -
   id: 1002
   issue_id: 15
   project_id: 1001
   project_board_id: 1001
+  sorting: 0

models/fixtures/project_board.yml

@@ -4,6 +4,7 @@
   title: To Do
   creator_id: 2
   default: true
+  sorting: 0
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -12,6 +13,7 @@
   project_id: 1
   title: In Progress
   creator_id: 2
+  sorting: 1
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -20,6 +22,7 @@
   project_id: 1
   title: Done
   creator_id: 2
+  sorting: 2
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -28,6 +31,7 @@
   project_id: 4
   title: Done
   creator_id: 2
+  sorting: 0
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -37,6 +41,7 @@
   title: Backlog
   creator_id: 2
   default: true
+  sorting: 0
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -46,6 +51,7 @@
   title: Backlog
   creator_id: 2
   default: true
+  sorting: 1
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -55,6 +61,7 @@
   title: Done
   creator_id: 2
   default: false
+  sorting: 0
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -64,6 +71,7 @@
   title: Backlog
   creator_id: 2
   default: true
+  sorting: 0
   created_unix: 1588117528
   updated_unix: 1588117528
 
@@ -73,5 +81,6 @@
   title: Uncategorized
   creator_id: 2
   default: true
+  sorting: 1
   created_unix: 1588117528
   updated_unix: 1588117528

models/fixtures/project_issue.yml

@@ -3,21 +3,25 @@
   issue_id: 1
   project_id: 1
   project_board_id: 1
+  sorting: 0
 
 -
   id: 2
   issue_id: 2
   project_id: 1
   project_board_id: 0 # no board assigned
+  sorting: 0
 
 -
   id: 3
   issue_id: 3
   project_id: 1
   project_board_id: 2
+  sorting: 0
 
 -
   id: 4
   issue_id: 5
   project_id: 1
   project_board_id: 3
+  sorting: 0