feat(pulls): add ci status field to pull request list (#956)

## Summary

- Add `"ci"` as a new selectable field for `tea pr list --fields`, allowing users to see CI status across multiple PRs at a glance
- Fetch CI status via `GetCombinedStatus` API **only when the `ci` field is explicitly requested** via `--fields`, avoiding unnecessary API calls in default usage
- Improve CI status display in both detail and list views:
  - **Detail view** (`tea pr <index>`): show each CI check with symbol, context name, description, and clickable link to CI run
  - **List view** (`tea pr list --fields ci`): show symbol + context name per CI check (e.g., `✓ lint, ⏳ build, ❌ test`)
  - **Machine-readable output**: return raw state string (e.g., `success`, `pending`)
- Replace pending CI symbol from `⭮` to `⏳` for better readability
- Extract `formatCIStatus` helper and reuse it in `PullDetails` to reduce code duplication
- Add comprehensive tests for CI status formatting and PR list integration

## Detail View Example

```
- CI:
  - ✓ [**lint**](https://ci.example.com/lint): Lint passed
  - ⏳ [**build**](https://ci.example.com/build): Build is running
  - ❌ [**test**](https://ci.example.com/test): 3 tests failed
```

## List View Example

```
INDEX  TITLE       STATE  CI
123    Fix bug     open   ✓ lint, ⏳ build, ❌ test
```

## Usage

```bash
# Show CI status column in list
tea pr list --fields index,title,state,ci

# Default output is unchanged (no CI column, no extra API calls)
tea pr list
```

## Files Changed

- `cmd/pulls/list.go` — conditionally fetch CI status per PR when `ci` field is selected
- `modules/print/pull.go` — add `ci` field, `formatCIStatus` helper, improve detail/list CI display
- `modules/print/pull_test.go` — comprehensive tests for CI status formatting

## Test plan

- [x] `go build ./...` passes
- [x] `go test ./...` passes (11 new tests)
- [x] `tea pr list` — default output unchanged, no extra API calls
- [x] `tea pr list --fields index,title,state,ci` — CI column with context names
- [x] `tea pr <index>` — CI section shows each check with name, description, and link
- [x] `tea pr list --fields ci -o csv` — machine-readable output shows raw state strings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://gitea.com/gitea/tea/pulls/956
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-committed-by: Bo-Yi Wu <appleboy.tw@gmail.com>

cmd/pulls/list.go

@@ -5,6 +5,8 @@ package pulls
 
 import (
 	stdctx "context"
+	"fmt"
+	"slices"
 
 	"code.gitea.io/sdk/gitea"
 	"code.gitea.io/tea/cmd/flags"
@@ -43,7 +45,8 @@ func RunPullsList(_ stdctx.Context, cmd *cli.Command) error {
 		return err
 	}
 
-	prs, _, err := ctx.Login.Client().ListRepoPullRequests(ctx.Owner, ctx.Repo, gitea.ListPullRequestsOptions{
+	client := ctx.Login.Client()
+	prs, _, err := client.ListRepoPullRequests(ctx.Owner, ctx.Repo, gitea.ListPullRequestsOptions{
 		ListOptions: flags.GetListOptions(cmd),
 		State:       state,
 	})
@@ -56,5 +59,21 @@ func RunPullsList(_ stdctx.Context, cmd *cli.Command) error {
 		return err
 	}
 
-	return print.PullsList(prs, ctx.Output, fields)
+	var ciStatuses map[int64]*gitea.CombinedStatus
+	if slices.Contains(fields, "ci") {
+		ciStatuses = map[int64]*gitea.CombinedStatus{}
+		for _, pr := range prs {
+			if pr.Head == nil || pr.Head.Sha == "" {
+				continue
+			}
+			ci, _, err := client.GetCombinedStatus(ctx.Owner, ctx.Repo, pr.Head.Sha)
+			if err != nil {
+				fmt.Printf("error fetching CI status for PR #%d: %v\n", pr.Index, err)
+				continue
+			}
+			ciStatuses[pr.Index] = ci
+		}
+	}
+
+	return print.PullsList(prs, ctx.Output, fields, ciStatuses)
 }