feat(miner): add a metrics command for the prediction Prometheus renderer

[real-venus]

Summary

• A fully-built, pure Prometheus text-exposition renderer for the miner's own prediction accuracy (renderMinerPredictionMetrics in packages/gittensory-engine/src/miner-prediction-metrics.ts) already existed, explicitly designed for cron/scrape use — but nothing in the CLI ever called it (Wire the existing miner-prediction Prometheus renderer into a real command #4838).
• Adds a gittensory-miner metrics subcommand that reads the local prediction ledger, pairs each prediction with its realized PR outcome (event-ledger pr_outcome events, latest per PR) to mark it correct/incorrect, maps the rows to the renderer's shape, and writes the renderer's Prometheus output to stdout — suitable for a scrape wrapper or a cron redirect.
• Per the issue's boundary, the renderer itself is unchanged — this only wires it into a command. The subcommand is read-only (opens both local stores read-only and closes them).
• Predictions without a realized outcome still count toward gittensory_miner_predictions_total (by conclusion) but not toward correct/incorrect, so the surface is meaningful before outcome-pairing exists and grows once it does.

Scope

• The PR title follows type(scope): short summary Conventional Commit format.
• This PR is focused and does not mix unrelated backend, UI, MCP, docs, dependency, and deploy changes.
• This follows CONTRIBUTING.md and does not reintroduce GitHub Pages, VitePress, site/, or CNAME.
• I linked a currently open issue this PR resolves — Closes Wire the existing miner-prediction Prometheus renderer into a real command #4838.

Validation

• git diff --check
• npm run typecheck
• npm run test:coverage — verified the new prediction-metrics-cli.js at 100% line + branch coverage locally via the v8 JSON report; 4 unit tests cover the prediction→outcome pairing (correct/incorrect/unresolved), the latest-outcome-per-PR dedup, skipping non-outcome and malformed events, the well-formed empty-ledger surface, and the unknown-option path.
• npm run command-reference:check (green — the added help line does not desync the generated command reference).

If any required check was skipped, explain why:

• actionlint, test:workers, build:mcp / test:mcp-pack, ui:openapi:check, ui:lint / ui:typecheck / ui:build, and npm audit were not run because this change touches only packages/gittensory-miner/** and test/** — no workflow, worker, MCP, OpenAPI/API, UI, or dependency surface for those jobs. The full npm run test:ci runs all of them on CI.

Safety

• No secrets, wallet details, hotkeys, coldkeys, user PATs, private keys, raw trust scores, private rankings, or private maintainer evidence are exposed. The output aggregates the operator's own local prediction/outcome tallies into standard Prometheus counters.
• Public GitHub text stays sanitized, low-noise, and does not imply compensation guarantees or optimization tactics.
• Public docs/changelogs are updated where needed; no changelog is edited (this is not a release-prep PR).

Auth/CORS/session, API/OpenAPI/MCP, and UI safety boxes are not applicable — this PR changes none of those surfaces.

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[real-venus]

Closing as a duplicate — #4838 was already resolved by #5470, which merged first. Thanks!