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>

claude_bottle/cli/resume.py

@@ -29,12 +29,6 @@ def cmd_resume(argv: list[str]) -> int:
     parser = argparse.ArgumentParser(prog=f"{PROG} resume", add_help=True)
     parser.add_argument("--dry-run", action="store_true")
     parser.add_argument("--remote-control", action="store_true")
-    parser.add_argument(
-        "--format",
-        choices=("text", "json"),
-        default="text",
-        help="preflight output format; --format=json requires --dry-run",
-    )
     parser.add_argument(
         "identity",
         help="bottle identity from a prior `start` (see its session-end output)",
@@ -61,6 +55,5 @@ def cmd_resume(argv: list[str]) -> int:
     return _launch_bottle(
         spec,
         dry_run=args.dry_run,
-        output_format=args.format,
         remote_control=args.remote_control,
     )