refactor(cli): drop --format=json end-to-end

Companion to the compact preflight in #31 — the JSON format was
the structured alternative to the verbose text summary. With the
new compact text already on screen, no consumer was using the
JSON shape, and the abstract `BottlePlan.to_dict` was the
biggest piece of API surface no one is implementing against.

Removed:
  - `--format` CLI flag from `start` and `resume`.
  - `output_format` kwarg from `_launch_bottle`.
  - `BottlePlan.to_dict` abstract method.
  - `DockerBottlePlan.to_dict` (60-line dict builder).
  - The `_PlanView` dataclass — `print` was the only remaining
    caller, so the env-name computation is inlined.
  - `tests/integration/test_dry_run_plan.py` (JSON-shape
    integration test).
  - `tests/unit/test_cli_start_format.py` (flag-conflict unit).

Plan-introspection is still possible by reading the
`DockerBottlePlan` dataclass directly — fields like `image`,
`container_name`, `stage_dir`, `use_runsc` are all there. Tooling
that needs a stable wire shape can JSON-serialize the dataclass
themselves.

411 unit + integration tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/unit/test_cli_start_format.py

@@ -1,54 +0,0 @@
-"""Unit: argparse-level CLI checks for `start --format`.
-
-Lives in tests/unit/ because nothing here touches Docker — the CLI
-exits at argument-validation time before any backend code runs.
-"""
-
-import json
-import os
-import subprocess
-import sys
-import tempfile
-import unittest
-from pathlib import Path
-
-REPO_ROOT = Path(__file__).resolve().parent.parent.parent
-
-
-class TestStartFormatFlag(unittest.TestCase):
-    def test_json_format_requires_dry_run(self):
-        """Emitting JSON in a real run would race the y/N prompt; the
-        CLI must reject the combination with a message that names the
-        offending flag."""
-        work_dir = Path(tempfile.mkdtemp())
-        try:
-            (work_dir / "claude-bottle.json").write_text(json.dumps({
-                "bottles": {"dev": {}},
-                "agents": {"demo": {"skills": [], "prompt": "", "bottle": "dev"}},
-            }))
-            env = os.environ.copy()
-            env["HOME"] = str(work_dir)
-            env.pop("CLAUDE_BOTTLE_DRY_RUN", None)
-            result = subprocess.run(
-                [
-                    sys.executable, str(REPO_ROOT / "cli.py"),
-                    "start", "--format", "json", "demo",
-                ],
-                cwd=work_dir,
-                env=env,
-                capture_output=True,
-                text=True,
-                check=False,
-            )
-            self.assertNotEqual(0, result.returncode)
-            self.assertIn(
-                "--format=json requires --dry-run", result.stderr,
-                f"expected the flag-conflict message; got stderr={result.stderr!r}",
-            )
-        finally:
-            import shutil
-            shutil.rmtree(work_dir, ignore_errors=True)
-
-
-if __name__ == "__main__":
-    unittest.main()