feat: add quick install script and packaging (#197)

Give bot-bottle a real distribution path so new users can install
without cloning the repo:

- pyproject.toml: full project metadata, a `bot-bottle` console-script
  entry point (bot_bottle.cli:main), and package-data for the runtime
  assets (Dockerfiles, egress entrypoint, netpool defaults, macos init).
  Still zero runtime pip dependencies.
- install.sh: POSIX, sudo-free, idempotent bootstrapper — checks Python
  >= 3.11, creates ~/.bot-bottle/{agents,bottles,contrib}, installs via
  pipx (pip --user fallback), then runs `bot-bottle doctor`.
- `bot-bottle doctor`: new store-free subcommand reporting Python
  version, backend availability (reuses is_backend_available rather than
  hardcoding Docker), and config-dir presence. Exits non-zero when a hard
  prerequisite is unmet.
- PRD prd-new-install-script and unit tests for doctor, the packaging
  contract, and the install script.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/cli/commands/__init__.py

@@ -21,6 +21,7 @@ _HANDLERS: dict[str, str] = {
     "backend": "backend:cmd_backend",
     "cleanup": "cleanup:cmd_cleanup",
     "commit": "commit:cmd_commit",
+    "doctor": "doctor:cmd_doctor",
     "edit": "edit:cmd_edit",
     "help": "help:cmd_help",
     "init": "init:cmd_init",
@@ -53,6 +54,6 @@ COMMANDS = {name: _lazy(spec) for name, spec in _HANDLERS.items()}
 # gating it on the schema breaks preflight on a fresh CI runner where stdin
 # isn't a TTY and the migration prompt can't be answered. `help` and `login`
 # likewise never touch the store.
-NO_MIGRATION_COMMANDS = frozenset({"backend", "help", "login"})
+NO_MIGRATION_COMMANDS = frozenset({"backend", "doctor", "help", "login"})
 
 __all__ = ["COMMANDS", "NO_MIGRATION_COMMANDS"]