Support SCP-style Git URLs without user@ prefix

[turian]

Summary

parse() crashes with AttributeError on SCP-style Git URLs without a user prefix (e.g., github.com:owner/repo.git). These are commonly produced by credential sanitization layers that strip user@ from remote URLs.

Root cause

All SSH regex patterns require user@ before the domain — either hardcoded git@ (GitHub, Bitbucket, Assembla) or a mandatory capture group (GitLab, Base).

Changes

SSH pattern fix (all 5 platforms):

• user@ is now optional via (?:(?P<_user>[^@]+)@)?, defaulting to the platform's configured user (typically "git")
• Added (?:...://|(?!.*://)) alternation to prevent git:// and https:// URLs from incorrectly matching SSH patterns (previously git@ served as an implicit anchor)
• Domain character classes tightened to [^/:@]+ to reject malformed inputs like @github.com:Org/Repo.git

False-positive hardening:

• BasePlatform SSH domain now requires a dot (FQDN) — rejects generic host:path like foo:bar, localhost:repo, C:\repo
• GitLab SSH owner excludes colon ([^/:]+) — prevents regex backtracking from parsing host:/repo.git with owner=":"

GitLab port format fix:

• GitLab GIT format now uses %(port_colon)s instead of %(port)s — fixes git://host.org:9999/... output (was git://host.org9999/...)

Files changed

File	Change
platforms/github.py	Optional user, protocol disambiguation, tighter domain
platforms/gitlab.py	Optional user, protocol disambiguation, owner excludes :, GIT port format fix
platforms/bitbucket.py	Optional user, protocol disambiguation, tighter domain
platforms/assembla.py	Optional user, protocol disambiguation, tighter domain
platforms/base.py	Optional user, FQDN-only domain, :// negative lookahead
result.py	port_colon format helper
tests/test_parse.py	+11 valid parse cases, +6 invalid input guards
tests/test_rewrite.py	+14 rewrite round-trip cases

Test plan

• All existing tests pass (no regressions)
• Userless SCP-style: github.com:Org/Repo.git, bitbucket.org:Org/Repo.git, host.org:Org/Repo.git, host.org:9999/Org/Repo.git, git.assembla.com:SomeRepoID.git
• Non-git SSH users: alice@github.com:Org/Repo.git, alice@host.org:Org/Repo.git, bob@git.assembla.com:SomeRepoID.git
• Explicit SSH scheme: ssh://alice@host.org/Org/Repo.git
• GitLab port variants: alice@host.org:9999/Org/Repo.git, ssh://git@host.org:9999/Org/Repo.git
• Unknown host fallback: git.example.com:team/repo.git → gitlab
• Rewrite round-trips: userless SCP → ssh, https, git for GitHub, GitLab, Bitbucket, Assembla
• Invalid inputs rejected: foo:bar, a:b, localhost:repo, C:\repo, host:/repo.git, :Org/Repo.git
• @github.com:Org/Repo.git (@ without username) remains invalid
• Non-SSH protocols (git://, https://) unaffected

🤖 Generated with Claude Code

[protoroto]

@turian Hi, thanks for opening this pr! In order to make the CI pass may I ask you to:

• open an issue (if it's not already opened)
• add a changes/<number-of-issue-created>.feature file with a brief explaination of what's in this pr, so that when it will be merged and released this message will appear in the changelog
  Thanks again!