chore(miner-foundation): wire gittensory-engine and gittensory-miner builds into CI

[JSONbored]

Extend .github/workflows/ci.yml's existing path-filter + conditional-step pattern (currently backend/ui/mcp/rees filters, each gating its own build/test steps) with two new filter keys — engine (paths: packages/gittensory-engine/**) and miner (paths: packages/gittensory-miner/**) — and matching conditional steps that run npm run build --workspace @jsonbored/gittensory-engine, the engine's own test suite, node --check (or tsc --noEmit) over the miner CLI, and the new npm run test:engine-parity script from the parity-suite issue. Also add both new scripts to the root test:ci chain so a push-to-main run (which always runs everything, per the existing github.event_name == 'push' fallback in every conditional) always exercises them, not only PRs that happen to touch those paths.

Deliverables

• .github/workflows/ci.yml changes job gains engine and miner filter outputs (new filters: block entries, paths packages/gittensory-engine/** and packages/gittensory-miner/** respectively).
• New conditional steps Build engine package / Engine test suite / Build miner CLI / Miner CLI check, each gated on github.event_name == 'push' || needs.changes.outputs.engine == 'true' (or .miner for the miner steps) — mirroring the exact conditional shape already used for the mcp filter's Build MCP/MCP package check steps.
• Root package.json gains build:engine, test:engine (or folds into the existing test:unit/test:coverage scope if the engine package's tests live under the root test/ tree rather than its own — confirm and match whichever the engine-package-skeleton issue actually established), and build:miner scripts.
• test:ci's chain in package.json (currently ending ... && npm run ui:lint && npm run ui:typecheck && npm run ui:test && npm run ui:build) gains the new build:engine/build:miner/test:engine-parity steps in a sensible position (alongside the existing build:mcp && npm run test:mcp-pack pair, since they're the closest existing analogue).
• A local run of npm run test:ci (or at minimum the new scripts in isolation) confirmed green before opening the PR.

References

• .github/workflows/ci.yml (changes job, lines ~30-55; the mcp filter's conditional steps, lines ~156-163) — the exact pattern to replicate for engine/miner.
• package.json test:ci script (line 62) — the chain to extend.
• packages/gittensory-engine/, packages/gittensory-miner/ — created by earlier issues in this phase (both must land first, since this issue only wires their ALREADY-EXISTING build/test scripts into CI, it does not create new ones).

[linear-code]

JSO-2394