fix: first-run person path and honest --confirm, --sim, and go copy

[DLANSAMA]

Why

A Bambu owner who has never used a CLI should get from pip install platecli to a first print without being routed into the agent workflow or told something false on the way. Post-0.5.0, several places did exactly that:

• bare plate off a TTY was a 20-subcommand argparse dump (exit 5)
• README hero and manual led with plate job <url> --confirm; the manual buried humans under Installing from source / Use with AI agents
• --confirm copy implied "leave it off and nothing on the printer moves", which is false for job/send (they still upload, exit 0, uploaded_not_printed)
• plate go help said "no slicer knowledge needed" while shelling out to OrcaSlicer
• --sim help was just "Enable simulation mode"
• every expected failure was logged twice; the missing-Orca error came with a contradictory "update config.json / tools/" INFO; the HTML-page error's next-step hint was unreachable dead code

What

Docs + CLI copy / error strings only. No version bump, no tag, no new feature.

• Bare plate off a TTY prints a short four-step first-run guide on stderr (install OrcaSlicer — a second slicer, not Bambu Studio; LAN mode + IP/serial/LAN access code, which is not the account password and rotates; plate setup; plate go). Still exit 5, stdout empty, never launches go/tui. A TTY still opens the wizard; --json keeps the error envelope.
• README / manual lead with that person path; plate job <url> --confirm moves under Scripts and agents. Manual Contents starts with Your first print.
• --confirm honesty per command, in README, manual, and the job/send --confirm help.
• plate go help / docs: OrcaSlicer still slices; you just never learn its flags.
• --sim help: fake printer, no hardware, no printer config, not a protocol test.
• go/tui non-TTY refusal points scripts at plate job <url> --json and says --confirm is what starts a print (or plate --sim status). Troubleshooting quotes the new line.
• Errors print once: emit_json_error already logs, then cli.main logged the same BambuError again. BambuError/abort gain a logged flag that emit_json_error sets; cli.main skips the re-log. Fixes all 52 call sites at once; plain abort(...) raises are still logged once by cli.main.
• Missing-Orca: contradictory INFO dropped when no install exists (the "Detected OrcaSlicer at …" INFO stays). HTML-page error names a good source (https://example.com/model.stl, a Printables page, or a local file). plate doctor with no printer points at plate preflight and plate --sim status.

Verification (local, matching ci.yml pins)

• ruff check / ruff format --check / mypy -p bambu_cli / bandit -ll / gen_schemas.py --check / check_layers.py: pass
• syntax, cli_help, ci_workflow, python_compat, privacy, release_readiness, agent_cli smokes: pass
• python -W error::ResourceWarning -m pytest tests/ -m "not live" --cov-fail-under=86: 1530 passed, coverage 90.96%
• Real CLI runs from source (--sim, tests/fixtures/cube.stl, a loopback HTML page): bare plate shows the guide; missing-Orca and HTML-page errors print exactly one ERROR line with the next step; go/tui/doctor show the new copy. No printer, no --confirm.

New tests: tests/test_first_run_path.py (26 tests) plus one in test_download_cmd.py; agent_cli_smoke.py and two bare-plate contract tests updated to the new contract.

Note: uv.lock on main still records platecli 0.5.0 after the 0.6.0.dev0 bump — uv run rewrites it locally. Left untouched here (out of scope).