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`.

coderd/database/queries/chats.sql

@@ -364,6 +364,13 @@ INSERT INTO chat_diff_statuses (
     additions,
     deletions,
     changed_files,
+    author_login,
+    author_avatar_url,
+    base_branch,
+    pr_number,
+    commits,
+    approved,
+    reviewer_count,
     refreshed_at,
     stale_at
 ) VALUES (
@@ -376,6 +383,13 @@ INSERT INTO chat_diff_statuses (
     @additions::integer,
     @deletions::integer,
     @changed_files::integer,
+    sqlc.narg('author_login')::text,
+    sqlc.narg('author_avatar_url')::text,
+    sqlc.narg('base_branch')::text,
+    sqlc.narg('pr_number')::integer,
+    sqlc.narg('commits')::integer,
+    sqlc.narg('approved')::boolean,
+    sqlc.narg('reviewer_count')::integer,
     @refreshed_at::timestamptz,
     @stale_at::timestamptz
 )
@@ -389,6 +403,13 @@ SET
     additions = EXCLUDED.additions,
     deletions = EXCLUDED.deletions,
     changed_files = EXCLUDED.changed_files,
+    author_login = EXCLUDED.author_login,
+    author_avatar_url = EXCLUDED.author_avatar_url,
+    base_branch = EXCLUDED.base_branch,
+    pr_number = EXCLUDED.pr_number,
+    commits = EXCLUDED.commits,
+    approved = EXCLUDED.approved,
+    reviewer_count = EXCLUDED.reviewer_count,
     refreshed_at = EXCLUDED.refreshed_at,
     stale_at = EXCLUDED.stale_at,
     updated_at = NOW()