Build QStringList separately before passing to QCommandLineOption
constructor to avoid formatting differences between local clang-format
and CI's clang-format v18.

P1: argv subcommand not stripped — QCommandLineParser saw the subcommand
name (e.g., "list") as the first positional argument, so every handler
tried to open a file named after the subcommand instead of the archive.
Fix: add positionalArgs() helper that strips the subcommand name.

P1: verify double-advanced file pointer — iterateHeaders() unconditionally
seeked past file content after the callback, but the verify callback
already consumed the content via processFileContentStreaming(). The
double-advance corrupted the archive position for subsequent headers.
Fix: iterateHeaders() now checks if the callback already consumed the
content before seeking, by comparing position before and after callback.

P2: getArchiveInfo() now propagates iterateHeaders() success/failure
via a scanComplete field instead of silently ignoring errors.

- Use normalizePath() consistently in extractSingleFile() instead of
  manual ./ stripping (was inconsistent with list and verify handlers)
- Surface processError details in verify's error status instead of
  silently discarding the decryption/decompression error message
- Include error field in verify JSON output when streaming fails

Three workstreams shipping as one coherent "agent-ready" feature:

Help system:
- Custom --help output listing all 7 subcommands with descriptions,
  global options, exit codes, and usage examples
- Intercepted before QApplication to prevent QCommandLineParser's
  auto-help from showing the old GUI-mode help
- argc == 1 (no args) still launches GUI, not help

MCP server (traktor mcp):
- JSON-RPC 2.0 over stdin/stdout per MCP spec 2025-11-25
- Synchronous blocking loop, no Qt event loop needed
- 5 tools: list, info, extract, cat, verify with typed inputSchema
- Calls BackupFile APIs directly (not CLI handler fprintf)
- cat returns file content as text via QBuffer (no size limit)
- verify uses CrcDevice for streaming CRC without disk writes

install-cli (traktor install-cli):
- Creates /usr/local/bin/traktor symlink on macOS
- Uses osascript with administrator privileges for auth dialog
- Pre-flight checks: correct symlink (skip), wrong symlink (overwrite),
  regular file (refuse with error)
- Auto-registers MCP server in ~/.claude.json for Claude Code discovery
- Handles invalid JSON in existing config (backup + create new)
- GUI menu item: Tools > Install Command Line Tool...
- Linux: prints manual symlink instructions
- Windows: notes PATH is set by installer

New files: src/mcpserver.h/cpp, src/installcli.h/cpp
7 new tests (81 total, all passing)