feat: add owner/labels metadata to sessions

[Skippy-the-Magnificent-one]

Problem

Multiple OpenClaw sessions (e.g. #king-dev and #skippy-inbox) share the same monkeyproof instance on cc-king. When one session clears finished sessions, it kills the other's results. No way to tell who spawned what.

Solution

Add optional owner and labels fields to the session create API:

{
  "task": "...",
  "cwd": "...",
  "preset": "claude-opus",
  "owner": "king-dev",
  "labels": ["king-trading", "swarm-reviewer"]
}

• owner -- string identifying who spawned it (channel name, user, etc.)
• labels -- array of tags for filtering (repo name, swarm role, etc.)
• Add filter params to GET /sessions: ?owner=king-dev or ?label=king-trading
• DELETE should support ?owner=king-dev to only clear your own sessions

Interim

Using task prefix convention: [king-dev|king-trading] FIXER: ...

[Skippy-the-Magnificent-one]

Update: label should default to the repo name extracted from cwd (last segment of path). So if cwd is /home/skippy/Development/king/king-trading, label auto-sets to king-trading. Override with explicit label if needed.

owner is the spawning channel/session (e.g. king-dev, skippy-inbox).