#3768 feat(daemon): daemon status lists the registered provider plugins

Summary

Part 2 of 4 of #3755 (umbrella #3747), stacked on #3767. Blocked by #3748: do not merge before it.

• agent-device daemon status [--state-dir <path>] [--json] reads daemon.json without contacting the daemon and lists every provider it registered (builtin/store/embedder, active/failed, typed error.reason). A record whose pid/start time no longer names a live process reports running: false.
• plugins list --json still works without a daemon (it lists store selections), and when a daemon runs for the same --state-dir it also returns that daemon's inventory under daemon.
• daemon and plugins schema, usage and help updated; daemon stays out of MCP (mcpExposed: false).

agent-device daemon status --json
agent-device plugins list --json

Not in this PR: the failed inventory entry inside the provider-not-registered error. #3748 owns that error, so I'll add the entry after rebasing onto it.

9 files.

Validation

pnpm check:affected --run --head f8555c9010 (the stack top, which contains this layer): passed (exactCommit). CI owns integration, coverage and device lanes.

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