unic-spec-review S3: shared context — read existing comments + Landscape Brief

[orioltf]

Parent

Epic: #200 — unic-spec-review plugin.

What to build

Give the review the shared context it reasons from, computed once per run and injected into the agents that need it.

Two parts:

1. Existing Confluence comments. Extend the vendored atlassian-fetch with a Confluence comment-read path (footer and inline comments) so the review can take prior discussion on the page into account. Read-only.
2. Landscape Brief. Add landscape-detector, which derives a single Landscape Brief from repo manifests and file listing plus user-declared out-of-repo adjacent systems: detected stack, test setup and frameworks, available tooling, a reachable-prod flag, and the declared adjacent systems. The technology landscape is never hardcoded. The reviewer can declare adjacent systems (e.g. .NET services, the CMS) during intake.

The Landscape Brief is computed once during preflight and made available to inject into the Testability, Feasibility, Spec-versus-Live, and Non-functional agents (those agents arrive in S4; this slice produces and exposes the Brief plus the comment context). Mirrors how unic-pr-review computes Doc Context once and injects it.

Acceptance criteria

• atlassian-fetch can read existing Confluence comments (footer and inline) for a page via the REST API with injected fetch; read-only, no writes.
• Read comments are surfaced to the review context so the Gaps agent (and later agents) can account for prior discussion.
• landscape-detector produces a Landscape Brief from repo manifests + file listing + declared adjacent systems, with the stack/test-setup/tooling/reachable-prod/adjacent-systems fields; no hardcoded stack assumptions.
• The reviewer can declare out-of-repo adjacent systems during intake and they appear in the Brief.
• The Brief is computed once and exposed for injection into review agents (consumed fully in S4).
• node:test unit tests cover landscape-detector and the atlassian-fetch comment-read path with injected deps; no live services.
• PR adds CHANGELOG.md bullets under [Unreleased] and bumps the patch version; verify:changelog passes. No em dash in authored text (except the mandated CHANGELOG version header).

Blocked by

• unic-spec-review S1: skeleton tracer bullet — classify one URL, fetch page, one Gaps agent, write report #202 (S1 — vendored atlassian-fetch + classifier rails).