feat(notification): implement GetNotificationUnreadCount API

[hvn2k1]

Follows #2750

What this PR does

Implements the GetNotificationUnreadCount RPC: returns the requesting user's unread notification count, backing the bell badge in the console.

Background / Why this PR is needed

This is the last read-side API of the notification center besides mark-all-as-read. The badge count must always agree with the Unread tab, so it uses the identical definition: published, not soft-deleted, no read marker for the viewer, and only notifications published after the viewer's account was created.

Points

• The count is a single COUNT query with a correlated NOT EXISTS on notification_read — no fan-out rows, O(1) with respect to user count, per the RFC's read-time derivation design.
• The account-created bound reuses the same earliestAccountCreatedAt lookup as ListNotifications' UNREAD filter, guaranteeing badge/tab consistency.
• This branch is stacked on feat(notification): implement MarkNotificationsAsRead API #2750 (mark-as-read), which is approved but blocked from merging by the notify-success-to-slack required-check misconfiguration in the main ruleset; the first commits shown here belong to that PR and will disappear once it merges.
• MarkAllNotificationsAsRead is the only remaining stub.

[Copilot]

Pull request overview

Implements the remaining notification-center read-side capabilities needed by the console: (1) an unread-count RPC for the bell badge, and (2) the “mark as read” RPC (stacked from #2750) with storage support for both MySQL and Postgres.

Changes:

• Add GetNotificationUnreadCount RPC response field (count) and implement handler + storage count query using NOT EXISTS on notification_read and the earliest-account-created bound.
• Implement MarkNotificationsAsRead end-to-end (proto + API + MySQL/Postgres storage upsert SQL).
• Add/extend mocks and unit tests for the new storage and API behavior.

Reviewed changes

Copilot reviewed 14 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
proto/proto.lock	Locks updated proto schema for unread-count response and mark-as-read request fields/options.
proto/notification/service.proto	Adds count to unread-count response and defines ids for mark-as-read request with OpenAPI constraints.
pkg/notification/storage/postgres/sql/insert_notification_read.sql	Postgres upsert for inserting read markers guarded by published+not-deleted.
pkg/notification/storage/postgres/sql/count_unread_notifications.sql	Base COUNT query used by query builder for unread-count.
pkg/notification/storage/postgres/notification.go	Adds storage methods for marking reads and counting unread notifications.
pkg/notification/storage/postgres/notification_test.go	Adds unit tests for new Postgres storage methods.
pkg/notification/storage/notification.go	Extends NotificationStorage interface with mark-as-read and unread-count methods.
pkg/notification/storage/mysql/sql/insert_notification_read.sql	MySQL insert-ignore upsert for inserting read markers guarded by published+not-deleted.
pkg/notification/storage/mysql/sql/count_unread_notifications.sql	Base COUNT query used by query builder for unread-count.
pkg/notification/storage/mysql/notification.go	Adds storage methods for marking reads and counting unread notifications.
pkg/notification/storage/mysql/notification_test.go	Adds unit tests for new MySQL storage methods.
pkg/notification/storage/mock/notification.go	Updates generated mock to include the new storage interface methods.
pkg/notification/api/error.go	Adds invalid-arg and max-exceeded statuses for mark-as-read ids validation.
pkg/notification/api/api.go	Implements GetNotificationUnreadCount and MarkNotificationsAsRead handlers.
pkg/notification/api/api_test.go	Adds handler tests for mark-as-read and unread-count.
api-description/web-api.swagger.yaml	Updates OpenAPI description and schemas for unread-count response and mark-as-read request.

Files not reviewed (1)

• pkg/notification/storage/mock/notification.go: Generated file

Suppressed comments (4)

pkg/notification/storage/mysql/notification_test.go:1111

• QueryRowContext is variadic; this expectation does not include enough argument matchers for the constructed COUNT query (filters + NOT EXISTS). It should match the full argument list, otherwise the mock will not recognize the call.

				s.qe.(*mock.MockQueryExecer).EXPECT().QueryRowContext(
					gomock.Any(), gomock.Any(), gomock.Any(),
				).Return(row)

pkg/notification/storage/mysql/notification_test.go:1129

• Same issue as above: QueryRowContext is variadic, but this expectation only provides a single variadic matcher. The unread-count query passes multiple SQL args, so the mock call won’t match.

				s.qe.(*mock.MockQueryExecer).EXPECT().QueryRowContext(
					gomock.Any(), gomock.Any(), gomock.Any(),
				).Return(row)

pkg/notification/storage/postgres/notification_test.go:1141

• QueryRowContext is variadic; this expectation does not include enough argument matchers for the constructed COUNT query (filters + NOT EXISTS). It should match the full argument list, otherwise the mock will not recognize the call.

				s.qe.(*mock.MockQueryExecer).EXPECT().QueryRowContext(
					gomock.Any(), gomock.Any(), gomock.Any(),
				).Return(row)

pkg/notification/storage/postgres/notification_test.go:1159

• Same issue as above: QueryRowContext is variadic, but this expectation only provides a single variadic matcher. The unread-count query passes multiple SQL args, so the mock call won’t match.

				s.qe.(*mock.MockQueryExecer).EXPECT().QueryRowContext(
					gomock.Any(), gomock.Any(), gomock.Any(),
				).Return(row)

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[Ubisoft-potato]

Thanks! LGTM!