chore(apps): check the docs site and viewer in CI, and bind the viewer to the engine's types

[zz-plant]

First of the follow-ups to #37, which imported refract-docs and refract-ui into apps/docs and apps/ui. This covers step 2 of docs/repositories.md ("move the viewer") and the CI half of step 1. The docs deploy, the Python adapter and retiring the old repos come in separate PRs.

Nothing was checking the apps

Since #37, nothing has run the apps' lint, tests or builds:

• their workflows sat under apps/*/.github, which GitHub doesn't read
• the root vitest config excludes apps/

This PR adds two path-filtered workflows, kept separate from the engine gate:

• docs-site.yml runs the docs site's checks
• viewer.yml runs the viewer's checks, and also runs when packages/evidence-graph or docs/examples change, since those are what the viewer's contract checks against

The viewer's event types had drifted

apps/ui/src/types.ts kept its own copy of the engine's types. That copy:

• still listed claim_first_seen, claim_softened and the other claim_* names, which the engine renamed sentence_*
• lacked edit_cluster_detected and talk_activity_spike

As a result, the timeline colours keyed to the old names never applied.

The viewer now:

• imports EventType and EvidenceEvent from @refract-org/evidence-graph as types only (workspace:*). The bundle carries nothing from the engine and is about the same size: 30.8 kB, was 30.6 kB.
• keeps its event list as a Record<EventType, true>. Adding a fake type to the engine's EventType fails the viewer's build with "Property 'drift_probe' is missing" (tested, then reverted).
• colours weakening and strengthening wording from the event's directionSignal, since the engine no longer has claim_softened or claim_strengthened
• has tests/engine-contract.test.ts, which imports, lists and re-exports the engine output in docs/examples/ and an event of every type. It checks that each event comes out deep-equal to what went in.

Removed per-app scaffolding

• Removed: both apps' bun.lock, the docs site's package-lock.json, the .husky folders, the mise.toml files (identical to the root's), the prepare: husky scripts, and the dead .github folders. The docs site's CODEOWNERS named the same team as the root's.
• Kept: each app's .lintstagedrc.json (the root hook applies it, as this commit's own hook run shows), plus biome.json, .opencode, LICENSE and AGENTS.md.

Docs

The package links, both apps' AGENTS.md files, the root README, AGENTS.md, COMPATIBILITY.md and docs/repositories.md now say where each app lives and which workflow checks it. So do the site pages that told readers to clone refract-ui.

The public site URL is unchanged, and the site still deploys from refract-docs; the next PR moves that.

Verification

• Root gate: frozen install, build, biome ci packages/, typecheck, check:boundaries, test (408 passed, 9 live-API tests skipped), check:examples and check:release --pack all pass.
• apps/docs: lint, tests (103) and build pass.
• apps/ui: lint, tests (31) and build pass.

For a decision

apps/ui/LICENSE is an MIT licence ("Copyright (c) 2024 NextConsensus"), but its package.json declares AGPL-3.0, and docs/repositories.md planned AGPL-3.0. This PR changes neither.

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