refactor: Use db.Get[] instead of db.GetEngine(ctx).Get(bean) to avoid zero value fetching wrong database record (#37977)

This PR replaces a set of struct-based `Get` lookups with explicit
`db.Get` / `db.Exist` conditions in places where zero-value fields can
lead to ambiguous matches or incorrect records being returned.

The main goal is to make read paths deterministic and avoid accidentally
matching the wrong row when only part of a struct is populated.

### What changed

- replace many `db.GetEngine(ctx).Get(bean)` calls with explicit
`builder.Eq` conditions across models such as actions, admin tasks,
issues, pull requests, repositories, users, packages, redirects,
watches, stars, and follows
- use quoted column names where needed for reserved fields like `index`,
`type`, and `name`
- add dedicated user lookup helpers for:
  - primary email
  - OAuth login source / login name
- update sign-in and OAuth-related flows to use explicit individual-user
lookups instead of partially populated `User` structs
- tighten package property and Terraform lock lookups to avoid ambiguous
reads and updates
- keep existing fallback behavior where needed, while removing reliance
on zero-value struct matching

### User-facing impact

These changes primarily affect authentication and account lookup paths:

- email/username sign-in now re-fetches users through explicit keys
- OAuth2 auto-linking now resolves users by name or primary email
explicitly
- OAuth2 login/sync now looks up users by login source, login type, and
login name explicitly
- non-individual accounts are no longer implicitly matched through
partial user lookups in these flows

This should reduce the risk of incorrect account matches and make query
behavior more predictable across the codebase.

---------

Co-authored-by: bircni <bircni@icloud.com>

modules/packages/terraform/lock.go

@@ -79,13 +79,12 @@ func RemoveLock(ctx context.Context, packageID int64) error {
 }
 
 func updateLock(ctx context.Context, refID int64, value string, cond builder.Cond) error {
-	pp := packages_model.PackageProperty{RefType: packages_model.PropertyTypePackage, RefID: refID, Name: LockFile}
-	ok, err := db.GetEngine(ctx).Get(&pp)
+	pp, ok, err := db.Get[packages_model.PackageProperty](ctx, builder.Eq{"ref_type": packages_model.PropertyTypePackage, "ref_id": refID, "`name`": LockFile})
 	if err != nil {
 		return err
 	}
 	if ok {
-		n, err := db.GetEngine(ctx).Where("ref_type=? AND ref_id=? AND name=?", packages_model.PropertyTypePackage, refID, LockFile).And(cond).Cols("value").Update(&packages_model.PackageProperty{Value: value})
+		n, err := db.GetEngine(ctx).ID(pp.ID).And(cond).Cols("value").Update(&packages_model.PackageProperty{Value: value})
 		if err != nil {
 			return err
 		}