refactor: collapse strix/sandbox into strix/runtime; in-sandbox Caido bootstrap

The split between ``strix/sandbox/`` and ``strix/runtime/`` was
artificial — both were managing the same backend. ``strix/sandbox/``
also collided uncomfortably with the SDK's ``agents.sandbox.*``
namespace. ``runtime/`` (which matches ``STRIX_RUNTIME_BACKEND``) is
the canonical home for everything Docker / Daytona / K8s lifecycle.

While merging, also rip out two pieces of Docker-specific coupling:

- ``caido_bootstrap`` was POSTing ``loginAsGuest`` from the host via
  ``aiohttp`` to ``http://127.0.0.1:{forwarded_port}``. That assumed
  Docker port forwarding; Daytona / K8s expose ports differently.
  Now we ``session.exec`` curl from *inside* the container — the
  SDK's runtime-agnostic exec primitive — so any backend works as
  long as it implements ``exec``. The host-side Caido ``Client``
  still uses the runtime's exposed-port URL for post-bootstrap calls,
  but that goes through the SDK's own ``resolve_exposed_port``
  abstraction (also runtime-agnostic).

- The bootstrap retry loop now doubles as the readiness probe, so
  ``healthcheck.wait_for_tcp_ready`` (and the entire
  ``healthcheck.py`` module) goes away.

Drive-by simplification: drop ``caido_host_port`` plumbing entirely.
It was only piped through ``make_agent_context`` → child contexts
without ever being read; only ``caido_client`` is consumed.

Drops ``aiohttp`` runtime dep (it stays only as a transitive of the
Caido SDK).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -41,7 +41,6 @@ dependencies = [
   "requests>=2.32.0",
   "cvss>=3.2",
   "caido-sdk-client>=0.2.0",
-  "aiohttp>=3.10.0",
 ]
 
 [project.scripts]
@@ -99,7 +98,6 @@ module = [
     "cvss.*",
     "docker.*",
     "caido_sdk_client.*",
-    "aiohttp.*",
 ]
 ignore_missing_imports = true
 disable_error_code = ["import-untyped"]