feat: redistribution toggle

[sbackend123]

Checklist

• I have read the coding guide.
• My change requires a documentation update, and I have done it.
• I have added tests to cover my changes.
• I have filled out the description and linked the related issues.

Description

• Adds PUT /redistribution so operators can enable/disable participation in new redistribution rounds without restarting the node.
• Exposes current toggle state as enabled on GET /redistributionstate.
• When disabled, the agent skips sample/commit for new rounds; an already committed round still proceeds through reveal/claim.

Open API Spec Version Changes (if applicable)

Motivation and Context (Optional)

Related Issue (Optional)

#5313

Screenshots (if appropriate):

AI Disclosure

• This PR contains code that has been generated by an LLM.
• I have reviewed the AI generated code thoroughly.
• I possess the technical expertise to responsibly review the code generated in this PR.

[gacevicljubisa]

Implementation looks correct. A few suggestions:

1. Move the toggle onto the existing resource — the flag is already read from GET /redistributionstate, so the write belongs there too:

GET /redistributionstate
PATCH /redistributionstate {"enabled": false}

Matches the repo convention (PATCH /stamps/{batch_id}, /tags/{id}, /grantee/{address}). Tried it locally, tests green, diff net smaller.

2. If you take PATCH, add it to Access-Control-Allow-Methods (api.go:618) — currently "GET, HEAD, OPTIONS, POST, PUT, DELETE", so PATCH is blocked by preflight.

3. Expose a "safe to stop" flag on GET /redistributionstate — hasCommittedThisRound / hasRevealedThisRound. RoundData already holds CommitKey and HasRevealed. Without it, step 2 of #5313 is a ~12.7 min blind wait.

4. Add a redistribution_enabled gauge — while disabled, lastSelectedRound keeps advancing while lastPlayedRound stalls, so a disabled node looks identical to a broken one in Grafana.