[Bug]: Test-FeatureJsonMatchesFeatureDir was missing in common.ps1 — this was a missing function that caused setup-tasks.ps1 to fail.

### Bug Description

On start of `/speckit.tasks` in PowerShell environment, it attempts to call function
`Test-FeatureJsonMatchesFeatureDir`
An error is thrown and there is no such commandlet.

CoPilot eventually worked around the problem.

```shell
.\.specify\scripts\powershell\setup-tasks.ps1 -Json
C:\Code\private\app\.specify\scripts\powershell\setup-tasks.ps1 : The term
'Test-FeatureJsonMatchesFeatureDir' is not recognized as the name of a cmdlet, function, script file, or
operable program. Check the spelling of the name, or if a path was included, verify that the path is
correct and try again.
At line:1 char:1
+ .\.specify\scripts\powershell\setup-tasks.ps1 -Json
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Test-FeatureJsonMatchesFeatureDir:String) [setup-tasks.ps1]
, CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException,setup-tasks.ps1
```

### Steps to Reproduce

1: Run `/speckit.tasks`
2: Errors noted for missing function `Test-FeatureJsonMatchesFeatureDir`

The function checks if feature.json pins an existing feature directory, and if it does, branch naming validation gets skipped.

Since the function is missing from common.ps1, this validation logic can't run.

### Expected Behavior

No error should have been reported.

### Actual Behavior

```shell
.\.specify\scripts\powershell\setup-tasks.ps1 -Json
C:\Code\private\app\.specify\scripts\powershell\setup-tasks.ps1 : The term
'Test-FeatureJsonMatchesFeatureDir' is not recognized as the name of a cmdlet, function, script file, or
operable program. Check the spelling of the name, or if a path was included, verify that the path is
correct and try again.
At line:1 char:1
+ .\.specify\scripts\powershell\setup-tasks.ps1 -Json
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Test-FeatureJsonMatchesFeatureDir:String) [setup-tasks.ps1]
, CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException,setup-tasks.ps1
```

Since the function is missing from common.ps1, this validation logic can't run.

CoPilot eventually determined what the function should have returned and worked around the problem.

### Specify CLI Version

0.8.13

### AI Agent

GitHub Copilot

### Operating System

Windows 11 (10.0.26220)

### Python Version

Python 3.12.6

### Error Logs

```shell
.\.specify\scripts\powershell\setup-tasks.ps1 -Json
C:\Code\private\app\.specify\scripts\powershell\setup-tasks.ps1 : At
C:\Code\private\app\.specify\scripts\powershell\common.ps1:141 char:122
+ ... -Path $RepoRoot $pinnedRelative) -ErrorAction SilentlyContinue)?.Path
+ ~~~~~~
Unexpected token '?.Path' in expression or statement.
At C:\Code\private\app\.specify\scripts\powershell\common.ps1:142 char:102
+ ... h -LiteralPath $ActiveFeatureDir -ErrorAction SilentlyContinue)?.Path
+ ~~~~~~
Unexpected token '?.Path' in expression or statement.
At line:1 char:1
+ .\.specify\scripts\powershell\setup-tasks.ps1 -Json
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ParserError: (:) [setup-tasks.ps1], ParseException
+ FullyQualifiedErrorId : UnexpectedToken,setup-tasks.ps1
```

### Additional Context

This speckit was in-place upgraded from a previous version ~ 1 month old

从 .specify/scripts/powershell/common.ps1 以及 .specify/scripts/powershell/setup-tasks.ps1 中的调用开始。在 PowerShell 中使用 setup-tasks.ps1 -Json 重现失败，然后验证 Test-FeatureJsonMatchesFeatureDir 可用，并且功能目录验证在没有报告的命令错误或解析器错误的情况下完成。

由索引模型根据 Issue 内容生成。