Add skip SSH host key verification and fix self-hosted server support

[chriswritescode-dev]

Closes #120

Summary

• Fix ssh-keyscan exit code handling that prevented self-hosted Git servers from connecting
• Fix SCP-style SSH URLs with custom ports (git@host:port/path) being parsed incorrectly
• Add "Skip SSH host key verification" checkbox in Add Repository dialog
• Add "Trust for future connections" checkbox in SSH host key verification dialog
• Move GitCredential type to shared package for better code organization

Root Cause Fixes

ssh-keyscan exit code

The ssh-keyscan command returns exit code 1 when some key types aren't supported (common on self-hosted servers), even though valid keys are present in stdout. The previous code rejected non-zero exit codes entirely, so the SSH host key dialog never appeared.

Fixed by using ignoreExitCode: true and parsing stdout for valid key lines regardless of exit code.

SCP-style SSH URL port parsing

URLs like git@ai.lab:2222/repo.git were parsed incorrectly - the port 2222 was treated as part of the path (per SCP syntax rules, the colon is a path separator). This caused SSH to connect on port 22 instead of 2222.

Fixed by adding normalizeSSHUrl() which detects the git@host:port/path pattern and converts it to proper ssh://git@host:port/path format before any parsing occurs.

New Features

• Skip SSH Verification checkbox on Add Repository form - auto-accepts host keys for self-hosted/internal Git servers
• Trust for future checkbox on SSH host key dialog - persists trust so the dialog doesn't appear again

Changes

• backend/src/ipc/sshHostKeyHandler.ts - Fix keyscan parsing, add trustForFuture support
• backend/src/utils/git-auth.ts - Add normalizeSSHUrl() for SCP-style port handling
• backend/src/services/git-auth.ts - Normalize URLs before parsing, branch between auto-accept and interactive verification
• backend/src/services/repo.ts - Normalize URLs at clone entry point, accept skipSSHVerification param
• backend/src/routes/repos.ts - Thread skipSSHVerification from request body
• frontend/src/components/repo/AddRepoDialog.tsx - Add skip verification checkbox
• frontend/src/components/ssh/SSHHostKeyDialog.tsx - Add trust for future checkbox
• shared/src/schemas/repo.ts - Add skipSSHVerification to CreateRepoRequestSchema
• Moved GitCredential interface to shared package, updated all imports