refactor(rees): introduce modular analyzer manifests

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Context

REES analyzer work is currently conflict-prone because new analyzers tend to edit the same central files: review-enrichment/src/brief.ts, review-enrichment/src/types.ts, review-enrichment/src/render.ts, engine allow-lists, UI metadata, and shared tests.

This issue creates the modular substrate so future analyzer PRs can be isolated to their own analyzer folder instead of repeatedly colliding with each other.

Parent: #1499

Deliverables

• Add a per-analyzer manifest/descriptor pattern under review-enrichment/src/analyzers/<name>/.
• Move analyzer metadata into descriptors: name, category, cost class, default enabled state, external requirements, timeout/limit defaults, docs text, and renderer hook.
• Replace the hand-maintained analyzer registry in brief.ts with a registry built from analyzer descriptors.
• Keep existing analyzer names and response compatibility intact.
• Make new analyzer PRs touch their own analyzer module first, with central files avoided or generated.
• Document the contribution pattern for analyzer authors.

Requirements

• Do not add new analyzer behavior in this issue.
• Do not remove existing analyzers.
• Preserve current REES_ANALYZERS behavior.
• Keep the response schema backward compatible for the engine.
• Do not include secrets, request bodies, diffs, raw prompts, comments, tokens, or private configs in descriptors or logs.

Acceptance criteria

• Existing REES tests pass.
• At least two existing analyzers are represented through the new descriptor path as proof of pattern, or all analyzers are migrated if the patch stays manageable.
• Adding a new analyzer no longer requires manually editing every central runtime/render/config surface.
• The parent roadmap can point future analyzer issues at this pattern.

Validation

• npm run test:ci -- --runInBand review-enrichment/test or the closest focused REES test command available in the repo.
• npm run test:coverage if touched lines fall under covered src/** paths.

Ownership

Maintainer-only. No gittensor:* labels.