refactor: organize authentication domain

[mnriem]

Description

Organize authentication as a complete first-class domain package without treating it as a CLI command hierarchy.

• Move the shared GitHub HTTP helpers from specify_cli._github_http into specify_cli.authentication.github_http and migrate repository consumers to the canonical domain path.
• Keep the established authentication registry, provider, configuration, HTTP, and monkeypatch boundaries intact.
• Move authentication-owned tests and helpers under tests/specify_cli/authentication/, preserving every existing authentication test function exactly once.
• Verify wheel packaging includes the complete authentication package and excludes the obsolete top-level helper module.

This makes authentication source and test ownership consistent with other first-class domains while preserving runtime behavior and compatibility.

Testing

• Tested locally with uv run specify --help
• Ran the complete suite in this worktree's repository venv: .venv/bin/python -m pytest - 8,390 passed, 16 skipped (8,406 collected)
• Ran focused authentication tests: 239 passed
• Ran uvx ruff@0.15.0 check src tests
• Ran git diff --check
• Built and inspected the wheel for expected/obsolete module paths
• Tested with a sample project (not applicable; structural domain refactor with unchanged runtime behavior)

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (fill in the disclosure below)

AI disclosure: Posted on behalf of @mnriem by GitHub Copilot (model: GPT-5.6 Sol, autonomous); the structural code/test changes and this PR description were fully AI-drafted under user-directed scope and review.

[Copilot]

Copilot review overview

🟢 Approval recommended

The relocation is complete, internal references are consistent, and existing focused coverage follows the new module boundaries.

Review effort: Balanced
Findings: None

What changed in this PR

Moves GitHub HTTP utilities and authentication tests into the first-class authentication domain without changing behavior.

Changes:

• Migrates all consumers to specify_cli.authentication.github_http.
• Reorganizes authentication tests and shared helpers.
• Updates documentation and monkeypatch paths for the new structure.

File	Description
src/​specify_cli/​authentication/​github_http.py	Establishes the canonical domain module.
src/​specify_cli/​bundles/​sources.py	Updates bundle download helper import.
src/​specify_cli/​extensions/​__init__.py	Updates extension resolver import and documentation.
src/​specify_cli/​presets/​__init__.py	Updates preset resolver import.
src/​specify_cli/​presets/​command_add.py	Updates preset installation import.
src/​specify_cli/​workflows/​_commands.py	Updates workflow catalog import.
src/​specify_cli/​workflows/​command_add.py	Updates workflow installation import.
tests/​http_helpers.py	Corrects the relocated test reference.
tests/​specify_cli/​authentication/​__init__.py	Defines the authentication test package.
tests/​specify_cli/​authentication/​helpers.py	Houses authentication-specific test helpers.
tests/​specify_cli/​authentication/​test_authentication.py	Updates domain test terminology.
tests/​specify_cli/​authentication/​test_github_http.py	Updates imports and monkeypatch targets.
tests/​test_extensions.py	Uses the relocated authentication helper.
tests/​test_presets.py	Uses the relocated authentication helper.
tests/​test_upgrade.py	Uses the relocated authentication helper.

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