Add dashboard, OTLP pipeline, and demo agent instrumentation - #1

- dashboard/: Node server with OTLP ingestion, WebSocket broadcast,
  registry/user API backed by Postgres, and topology UI showing
  gateway allow/deny decisions in real time. Fixes registry query
  (principal_key_permissions has no subject_identity column) and
  Anthropic arrow highlight (only activates for api.anthropic.com,
  not denied mcp-proxy.anthropic.com requests).
- docker-compose.postgres.yml: add otel-collector service bridging
  gateway OTLP gRPC to dashboard HTTP/JSON.
- scripts/up.sh + down.sh: start/stop the full dev stack in one command.
- examples/demo-agent.sh: emit agent.requested + agent.prompted OTLP
  log events to the dashboard on prompt dispatch, lighting up the
  alice→agent-platform and agent-platform→agent topology edges.
- examples/register-principal-key.sh: flush transient TPM handles
  after tpm2_ptool init to prevent slot exhaustion on swtpm.
- .gitignore: exclude .run/, config.toml, certs/ (runtime state).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>