feat(review): add PR reviewer swarm agents (#1851)

* feat(review): add PR reviewer swarm agents

Seven read-only subagents coordinated by an orchestration skill for
structured, evidence-grounded production-readiness PR reviews.

Agents: facts-historian, branch-hygiene, risk-architect, test-ci-verifier,
security-boundary, docs-dod, synthesis-critic. All use Read/Grep/Glob/Bash
only — no edit tools.

Skill invoked as /gitnexus-pr-swarm-review <PR>.

* Address PR review feedback (#1851)

- Pin explicit model IDs in all 7 reviewer-swarm agents per CLAUDE.md
  (no unversioned aliases). Set the two mechanical agents
  (test-ci-verifier, branch-hygiene-reviewer) to claude-haiku-4-5-20251001
  per @Cenrax's "this could be haiku"; the five analytical agents use
  claude-sonnet-4-6.
- Add an explicit read-only Bash policy (permitted/prohibited command
  lists) to every agent's Rules section, so the read-only guarantee is
  defended against injected/adversarial PR content rather than prose-only.
- Add a hard synthesis-critic gate to the swarm skill: do not post the
  final review until the critic's "Required corrections before posting"
  section is empty (was advisory only).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(review): make PR reviewer swarm portable across AI CLIs

Restructure the reviewer swarm around a single CLI-neutral source of truth so it
runs from any AI CLI, not just Claude Code.

- pr-swarm-review/: canonical orchestration.md (Swarm + Solo execution modes with
  an identical output contract) and personas/0N-*.md (the 7 review personas,
  relocated verbatim from the Claude agents, each tagged with a model tier and the
  read-only Bash policy). Single source of truth — edit here, not in the wrappers.
- Thin per-CLI adapters that read the canonical spec at runtime (no duplication):
  - Claude Code: coordinator skill (Swarm mode) + the 7 agents are now thin
    wrappers that read their persona file (frontmatter/model preserved; mechanical
    lanes Haiku, analytical lanes Sonnet).
  - Gemini CLI: .gemini/commands/gitnexus-pr-swarm-review.toml
  - GitHub Copilot: .github/prompts/gitnexus-pr-swarm-review.prompt.md
  - Cursor: .cursor/commands/gitnexus-pr-swarm-review.md
- AGENTS.md: canonical "PR Swarm Review" section -> orchestration.md, the universal
  entrypoint honored by Codex, Cursor, Gemini, Copilot, and any AGENTS.md-aware
  agent (Codex user-level prompt install noted in the README).

Graceful degradation: only Claude Code has parallel subagents (Swarm mode); every
other CLI runs the 7 lanes sequentially in one agent (Solo mode) with the same
output contract. prettier --check clean (root config).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gemini/commands/gitnexus-pr-swarm-review.toml

@@ -0,0 +1,19 @@
+description = "GitNexus production-readiness PR swarm review (Solo mode)"
+
+prompt = """
+You are the GitNexus PR review coordinator. Review this pull request: {{args}}
+(a PR URL or number for https://github.com/abhigyanpatwari/GitNexus). If no target was
+given, ask for one.
+
+Read `pr-swarm-review/orchestration.md` in this repository and follow it exactly. It is the
+canonical, CLI-neutral review contract (lanes, classifications, output structure, finding
+format, hidden-Unicode checks, behavior rules).
+
+Run in **Solo mode**: you are a single agent, so perform all seven lanes yourself in
+dependency order, adopting each persona in `pr-swarm-review/personas/0N-*.md` in turn
+(lanes 1-2 first, then 3-6, then lane 7). Keep every lane's findings in context. Lane 7
+(synthesis critic) is a hard gate: do not emit the final review until its "Required
+corrections before posting" section is empty — revise and re-run it otherwise.
+
+Stay strictly read-only: investigate and report; never edit files, commit, or post to GitHub.
+"""