fix: catch NoSuchPathError in get_git_root()

[VoidChecksum]

Summary

• Add git.NoSuchPathError to the exception handler in get_git_root() so paths containing special characters (like $$ on Windows) don't cause an uncaught exception crash
• Add unit tests verifying get_git_root() returns None for both NoSuchPathError and InvalidGitRepositoryError

Root Cause

When a directory path contains $$ characters on Windows, GitPython's internal os.path.expandvars() silently corrupts the path (e.g., F:\$$data\python\detect_programs becomes F:\$data\python\detect_programs). The corrupted path doesn't exist on disk, so git.Repo() raises git.exc.NoSuchPathError. This exception was not in the except clause of get_git_root(), causing an uncaught exception crash at startup.

Fix

One-line change: add git.NoSuchPathError to the existing except tuple in get_git_root(), matching the existing pattern for git.InvalidGitRepositoryError and FileNotFoundError. This allows aider to gracefully fall back when the git repo path cannot be resolved.

Test plan

• Added test_get_git_root_no_such_path_error - mocks git.Repo to raise NoSuchPathError, verifies get_git_root() returns None
• Added test_get_git_root_invalid_repo - mocks git.Repo to raise InvalidGitRepositoryError, verifies existing behavior still works
• Both tests pass locally

Fixes #2957

[Copilot]

Pull request overview

This PR hardens get_git_root() against git.exc.NoSuchPathError (notably triggered on Windows when GitPython corrupts paths containing $$) so aider can gracefully start up and proceed without a resolved git root.

Changes:

• Catch git.NoSuchPathError in aider.main.get_git_root() and return None instead of crashing.
• Add unit tests ensuring get_git_root() returns None for both NoSuchPathError and InvalidGitRepositoryError.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
aider/main.py	Expands get_git_root() exception handling to include NoSuchPathError.
tests/basic/test_main.py	Adds tests covering NoSuchPathError and InvalidGitRepositoryError behaviors for get_git_root().

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