Fix: Enable git worktree support and improve pr create error handling (#850)

## Problem

Tea commands fail when run from git worktrees with the error:
Remote repository required: Specify ID via --repo or execute from a
local git repo.

Even though the worktree is in a valid git repository with remotes
configured.

Additionally, `tea pr create` was missing context validation, showing
cryptic errors like `"path segment [0]
is empty"` instead of helpful messages.

## Root Cause

1. **Worktree issue**: go-git's `PlainOpenWithOptions` was not
configured to read the `commondir` file that
git worktrees use. This file points to the main repository's `.git`
directory where remotes are actually
stored (worktrees don't have their own remotes).

2. **PR create issue**: Missing `ctx.Ensure()` validation meant errors
weren't caught early with clear
messages.

## Solution

### 1. Enable worktree support (`modules/git/repo.go`)
```go
EnableDotGitCommonDir: true, // Enable commondir support for worktrees

This tells go-git to:
- Read the commondir file in .git/worktrees/<name>/commondir
- Follow the reference (typically ../..) to the main repository
- Load remotes from the main repo's config

2. Add context validation (cmd/pulls/create.go)

ctx.Ensure(context.CtxRequirement{
LocalRepo:  true,
RemoteRepo: true,
})

Provides clear error messages and matches the pattern used in pr
checkout (fixed in commit 0970b945 from
2020).

3. Add test coverage (modules/git/repo_test.go)

- Creates a real git repository with a worktree
- Verifies that RepoFromPath() can open the worktree
- Confirms that Config() correctly reads remotes from main repo

Test Results

Without fix:
❌ FAIL: Should NOT be empty, but was map[]

With fix:
✅ PASS: TestRepoFromPath_Worktree (0.12s)

Manual test in worktree:
cd /path/to/worktree
tea pr create --title "test"
# Now works! ✅

Checklist

- Tested manually in a git worktree
- Added test case that fails without the fix
- All existing tests pass

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/850
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: Brandon Martin <brandon@codedmart.com>
Co-committed-by: Brandon Martin <brandon@codedmart.com>

cmd/pulls/create.go

@@ -42,6 +42,10 @@ var CmdPullsCreate = cli.Command{
 
 func runPullsCreate(_ stdctx.Context, cmd *cli.Command) error {
 	ctx := context.InitCommand(cmd)
+	ctx.Ensure(context.CtxRequirement{
+		LocalRepo:  true,
+		RemoteRepo: true,
+	})
 
 	// no args -> interactive mode
 	if ctx.NumFlags() == 0 {

modules/git/repo.go

@@ -24,7 +24,8 @@ func RepoFromPath(path string) (*TeaRepo, error) {
 		path = "./"
 	}
 	repo, err := git.PlainOpenWithOptions(path, &git.PlainOpenOptions{
-		DetectDotGit: true,
+		DetectDotGit:          true,
+		EnableDotGitCommonDir: true, // Enable commondir support for worktrees
 	})
 	if err != nil {
 		return nil, err

modules/git/repo_test.go

@@ -0,0 +1,63 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepoFromPath_Worktree(t *testing.T) {
+	// Create a temporary directory for test
+	tmpDir, err := os.MkdirTemp("", "tea-worktree-test-*")
+	assert.NoError(t, err)
+	defer os.RemoveAll(tmpDir)
+
+	mainRepoPath := filepath.Join(tmpDir, "main-repo")
+	worktreePath := filepath.Join(tmpDir, "worktree")
+
+	// Initialize main repository
+	cmd := exec.Command("git", "init", mainRepoPath)
+	assert.NoError(t, cmd.Run())
+
+	// Configure git for the test
+	cmd = exec.Command("git", "-C", mainRepoPath, "config", "user.email", "test@example.com")
+	assert.NoError(t, cmd.Run())
+	cmd = exec.Command("git", "-C", mainRepoPath, "config", "user.name", "Test User")
+	assert.NoError(t, cmd.Run())
+
+	// Add a remote to the main repository
+	cmd = exec.Command("git", "-C", mainRepoPath, "remote", "add", "origin", "https://gitea.com/owner/repo.git")
+	assert.NoError(t, cmd.Run())
+
+	// Create an initial commit (required for worktree)
+	readmePath := filepath.Join(mainRepoPath, "README.md")
+	err = os.WriteFile(readmePath, []byte("# Test Repo\n"), 0644)
+	assert.NoError(t, err)
+	cmd = exec.Command("git", "-C", mainRepoPath, "add", "README.md")
+	assert.NoError(t, cmd.Run())
+	cmd = exec.Command("git", "-C", mainRepoPath, "commit", "-m", "Initial commit")
+	assert.NoError(t, cmd.Run())
+
+	// Create a worktree
+	cmd = exec.Command("git", "-C", mainRepoPath, "worktree", "add", worktreePath, "-b", "test-branch")
+	assert.NoError(t, cmd.Run())
+
+	// Test: Open repository from worktree path
+	repo, err := RepoFromPath(worktreePath)
+	assert.NoError(t, err, "Should be able to open worktree")
+
+	// Test: Read config from worktree (should read from main repo's config)
+	config, err := repo.Config()
+	assert.NoError(t, err, "Should be able to read config")
+
+	// Verify that remotes are accessible from worktree
+	assert.NotEmpty(t, config.Remotes, "Should be able to read remotes from worktree")
+	assert.Contains(t, config.Remotes, "origin", "Should have origin remote")
+	assert.Equal(t, "https://gitea.com/owner/repo.git", config.Remotes["origin"].URLs[0], "Should have correct remote URL")
+}