fix: use SQL-level auth filtering for chat listing (#23159)

## Problem

The chat listing endpoint (`GetChatsByOwnerID`) was using
`fetchWithPostFilter`, which fetches N rows from the database and then
filters them in Go memory using RBAC checks. This causes a pagination
bug: if the user requests `limit=25` but some rows fail the auth check,
fewer than 25 rows are returned even though more authorized rows exist
in the database. The client may incorrectly assume it has reached the
end of the list.

## Solution

Switch to the same pattern used by `GetWorkspaces`, `GetTemplates`, and
`GetUsers`: `prepareSQLFilter` + `GetAuthorized*` variant. The RBAC
filter is compiled to a SQL WHERE clause and injected into the query
before `ORDER BY`/`LIMIT`, so the database returns exactly the requested
number of authorized rows.

Additionally, `GetChatsByOwnerID` is renamed to `GetChats` with
`OwnerID` as an optional (nullable) filter parameter, matching the
`GetWorkspaces` naming convention.

## Changes

| File | Change |
|------|--------|
| `queries/chats.sql` | Renamed to `GetChats`, `owner_id` now optional
via CASE/NULL, added `-- @authorize_filter` |
| `queries.sql.go` | Renamed constant, params struct (`GetChatsParams`),
and method |
| `querier.go` | Interface method renamed |
| `modelqueries.go` | Added `chatQuerier` interface +
`GetAuthorizedChats` impl |
| `dbauthz/dbauthz.go` | `GetChats` now uses `prepareSQLFilter` instead
of `fetchWithPostFilter` |
| `dbauthz/dbauthz_test.go` | Updated tests for SQL filter pattern |
| `dbmock/dbmock.go` | Renamed + added mock for `GetAuthorizedChats` |
| `dbmetrics/querymetrics.go` | Renamed + added metrics wrapper |
| `rbac/regosql/configs.go` | Added `ChatConverter` (maps `org_owner` to
empty string literal since `chats` has no `organization_id` column) |
| `rbac/authz.go` | Added `ConfigChats()` |
| `chats.go` | Handler uses renamed method with `uuid.NullUUID` |
| `searchquery/search.go` | Updated return type |
| `gitsync/worker.go` | Updated interface and call site |
| Various test files | Updated for renamed types |

coderd/database/queries/chats.sql

@@ -113,13 +113,16 @@ ORDER BY
     created_at ASC,
     id ASC;
 
--- name: GetChatsByOwnerID :many
+-- name: GetChats :many
 SELECT
     *
 FROM
     chats
 WHERE
-    owner_id = @owner_id::uuid
+    CASE
+        WHEN @owner_id :: uuid != '00000000-0000-0000-0000-000000000000'::uuid THEN chats.owner_id = @owner_id
+        ELSE true
+    END
     AND CASE
         WHEN sqlc.narg('archived') :: boolean IS NULL THEN true
         ELSE chats.archived = sqlc.narg('archived') :: boolean
@@ -143,6 +146,8 @@ WHERE
         )
         ELSE true
     END
+    -- Authorize Filter clause will be injected below in GetAuthorizedChats
+    -- @authorize_filter
 ORDER BY
     -- Deterministic and consistent ordering of all rows, even if they share
     -- a timestamp. This is to ensure consistent pagination.