feat: Right sidebar, auth system overhaul, save/draft workflow, and code snippet generator

[markkr125]

Summary

Major feature batch adding a right sidebar panel, a complete 14-type auth system with OAuth 2.0 support, save/draft request workflow, and an expanded code snippet generator covering 23 languages.

New Features

Right Sidebar (sidebar)

• Icon-rail sidebar with flyout panels for Variables and Code Snippets
• VariablesPanel — read-only view of active environment variables with local override indicators
• SnippetPanel — inline code snippet generator that live-updates as the request is edited, with language selector and copy-to-clipboard

Auth System (auth, auth_handler.py)

• FieldSpec-driven architecture supporting all 14 Postman auth types (API Key, Bearer, Basic, Digest, OAuth 1.0, OAuth 2.0, Hawk, AWS Signature, NTLM, Akamai EdgeGrid, ASAP/Atlassian, JWT Bearer, Session Token, Custom)
• Shared _AuthMixin used by both RequestEditor and FolderEditor with auth inheritance
• Generic auth_serializer for load/save across all types
• apply_auth() in auth_handler.py shared by HTTP send and snippet generation
• Full OAuth 2.0 flow with OAuth2Page (grant-type switching UI) and OAuth2Service (4 grant types: Authorization Code, Client Credentials, Password, Implicit)
• Hawk "Include payload hash" checkbox matching Postman behavior

Save & Draft Workflow

• SaveRequestDialog — save draft requests to a collection with folder picker
• _DraftControllerMixin — draft tab open/save lifecycle management
• New "+" button popup (NewItemPopup) in collection header for creating requests/collections

Code Snippet Generator (snippet_generator)

• Expanded from single file to sub-package covering 23 languages across 3 modules:
  • Shell: cURL, HTTP raw, wget, HTTPie, PowerShell
  • Dynamic: Python, JavaScript (fetch/XHR/jQuery), Node.js, Ruby, PHP, Dart
  • Compiled: Go, Rust, C, Swift, Java, Kotlin, C#
• Auth-aware snippet generation via shared apply_auth() path

UX Improvements

• Middle-click to close tabs
• Fixed startup race condition where loading screen could be skipped if collection fetch completed before signal wiring
• Deprecated QMouseEvent.pos() replaced with event.position().toPoint()

Stats

• 63 files changed, ~10,978 insertions, ~936 deletions
• 32 new files (source + tests)
• Test suite: 1,196 tests passing, lint/format/mypy clean