fix(cli): report argument errors through the --json contract

[ArcueidMP]

With --json, a command-line parsing failure currently prints clap's usage error to stderr and leaves stdout empty, so a caller reading the JSON contract sees no error at all. The case from the issue, --session given before the subcommand, is also misreported: clap suggests --version and prints Usage: bsk --version <COMMAND>.

Fixes #387.

• When --json appears in argv before --, clap failures are written to stdout as the usual flat error: code: "invalid_params", exit_code: 1, data.reason: "cli_parse_error". message is clap's summary on one line; data.details keeps the full clap text with tips and usage. The flag is read from raw argv because clap can stop before it reaches --json; a --json inside a value (--selector=--json) or after -- does not count.
• A misplaced --session / --tab-id gets a rebuilt clap error: the tip says the option belongs after a supporting subcommand, and the usage line is that of the command being parsed instead of one built around --version. The same text is the JSON hint.
• Human output, exit codes and help are otherwise unchanged: usage errors stay on stderr with exit 1, and --help / --version print text and exit 0 even with --json.
• Document flag placement and the parse-error shape in the CLI README. The new tests also run in the Windows job, since the report came from PowerShell with redirected stdout.

$ bsk --session s1 click --selector '#submit' --json
{
  "code": "invalid_params",
  "message": "unexpected argument '--session' found",
  "hint": "--session and --tab-id are command-specific options; place them after a subcommand that supports them, e.g. `bsk click --session <id> --tab-id <tab> --selector '#submit'`; run `bsk <cmd> --help` for supported options",
  "exit_code": 1,
  "data": {
    "details": "error: unexpected argument '--session' found\n\n  tip: --session and --tab-id are command-specific options; ...\n\nUsage: bsk [OPTIONS] <COMMAND>\n\nFor more information, try '--help'.",
    "reason": "cli_parse_error"
  }
}

--session and --tab-id are not made global, which the issue suggests first. Most commands require them and some do not accept them. A clap global argument cannot be required and would collide with each command's own --session, so commands would lose clap's per-command validation and help, and commands such as status would silently accept a session. --json, --quiet and --verbose were already global; a parse test now covers both placements.

Testing

• cargo test -p bsk --test cli_usage_errors --test cli_parse --locked: process-level coverage of stdout/stderr separation, exit codes, redirected stdout, non-UTF-8 argv, forced color, nested subcommands, and the -- / --flag=--json cases
• cargo test -p bsk --locked
• cargo fmt --all -- --check, cargo clippy -p bsk --all-targets --locked -- -D warnings