Implement SAND-WP-0002 meta-framework foundation (T01–T09)

Add meta-framework spec, pydantic schemas, profile/extension YAML, extension
registry, ext.compose-ssh backend, SandboxManager with State Hub events, CLI
commands, integration docs, capability registry entry, and compose-e2e runbook.
Nine unit tests pass. T10 remote smoke test remains for operator.

pyproject.toml

@@ -11,6 +11,9 @@ requires-python = ">=3.11"
 license = "MIT-0"
 dependencies = [
     "typer>=0.12",
+    "pydantic>=2.0",
+    "pyyaml>=6.0",
+    "httpx>=0.27",
 ]
 
 [project.scripts]