feat(gitsync): enrich PR status with author, base branch, review info (#23038)

## Summary

Adds 7 new fields to the PR status stored by gitsync, all sourced from
the existing GitHub API calls (**zero additional HTTP requests**):

| Field | Source | Purpose |
|---|---|---|
| `author_login` | `pull.user.login` | PR author username |
| `author_avatar_url` | `pull.user.avatar_url` | PR author avatar for UI
|
| `base_branch` | `pull.base.ref` | Target branch (e.g. `main`) |
| `pr_number` | `pull.number` | Explicit PR number |
| `commits` | `pull.commits` | Number of commits in PR |
| `approved` | Derived from reviews | True when ≥1 approved, no
outstanding changes requested |
| `reviewer_count` | Derived from reviews | Distinct reviewers with a
decisive state |

## Changes

- **`gitprovider/gitprovider.go`**: Added 7 fields to `PRStatus` struct.
- **`gitprovider/github.go`**: Expanded the anonymous struct in
`FetchPullRequestStatus` to decode new JSON fields. Replaced
`hasOutstandingChangesRequested()` with `summarizeReviews()` returning a
`reviewStats` struct with `changesRequested`, `approved`, and
`reviewerCount`.
- **Migration 000434**: Adds 7 columns to `chat_diff_statuses`.
- **`queries/chats.sql`**: Updated `UpsertChatDiffStatus`
INSERT/VALUES/ON CONFLICT.
- **`gitsync/gitsync.go`**: Maps new `PRStatus` fields into upsert
params.
- **`gitsync/worker.go`**: Maps new columns in row-to-model converter.
- **`codersdk/chats.go`**: Added fields to SDK `ChatDiffStatus` type.
- **`coderd/chats.go`**: Maps new DB fields in
`convertChatDiffStatus()`.
- Auto-generated: `models.go`, `queries.sql.go`, `dump.sql`,
`typesGenerated.ts`.

codersdk/chats.go

@@ -630,6 +630,13 @@ type ChatDiffStatus struct {
 	Additions        int32      `json:"additions"`
 	Deletions        int32      `json:"deletions"`
 	ChangedFiles     int32      `json:"changed_files"`
+	AuthorLogin      *string    `json:"author_login,omitempty"`
+	AuthorAvatarURL  *string    `json:"author_avatar_url,omitempty"`
+	BaseBranch       *string    `json:"base_branch,omitempty"`
+	PRNumber         *int32     `json:"pr_number,omitempty"`
+	Commits          *int32     `json:"commits,omitempty"`
+	Approved         *bool      `json:"approved,omitempty"`
+	ReviewerCount    *int32     `json:"reviewer_count,omitempty"`
 	RefreshedAt      *time.Time `json:"refreshed_at,omitempty" format:"date-time"`
 	StaleAt          *time.Time `json:"stale_at,omitempty" format:"date-time"`
 }