Add AgentGit M1: agent-native git layer over a Forgejo backend

AgentGit is a thin, DID-gated source-collaboration layer over a backend
forge (default Forgejo at git.profullstack.com, BBS-members-only) — not a
new git host. M1 implements the contract and engines:

- forge/adapter.ts: ForgeAdapter interface (only forge-specific surface)
- forge/forgejo.ts: ForgejoAdapter over Forgejo/Gitea REST v1 (injectable
  fetch, typed errors), incl. ensureUser for member provisioning
- access.ts: gateAccess DID membership gate (owner/role/visibility)
- merge-policy.ts: evaluateMergePolicy pure engine (reviews, reputation
  floor, checks, escrow, merge method, agent-merge toggle)
- service.ts: AgentGitService ties gate + policy to the adapter; refuses
  policy-failing merges; provisionMember hook for AgentBBS
- schemas: logicsrc-repo + logicsrc-pull-request, registered in
  @logicsrc/validators with fixtures
- docs/agentgit.md spec; plugin wired into root build (default/disabled)

27 vitest tests pass; full monorepo build green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugins/agentgit/src/domain.ts

@@ -0,0 +1,98 @@
+// Domain types for AgentGit, mirroring the LogicSRC repo and pull-request
+// schemas (packages/schemas/schemas/logicsrc-{repo,pull-request}.schema.json).
+
+export type MemberRole = "maintainer" | "contributor" | "reviewer" | "reader";
+export type MergeMethod = "merge" | "squash" | "rebase";
+export type Visibility = "members_only" | "private" | "public";
+export type ReviewDecision = "approve" | "request_changes" | "comment";
+export type CheckStatus = "pending" | "passing" | "failing";
+export type PullRequestStatus =
+  | "draft"
+  | "open"
+  | "approved"
+  | "changes_requested"
+  | "merged"
+  | "closed";
+
+export interface MergePolicy {
+  min_reviews: number;
+  require_passing_checks: boolean;
+  reviewer_reputation_min: number;
+  escrow_required: boolean;
+  allow_agent_merge: boolean;
+  allowed_merge_methods: MergeMethod[];
+}
+
+export const DEFAULT_MERGE_POLICY: MergePolicy = {
+  min_reviews: 1,
+  require_passing_checks: true,
+  reviewer_reputation_min: 0,
+  escrow_required: false,
+  allow_agent_merge: true,
+  allowed_merge_methods: ["squash"]
+};
+
+export interface RepoMember {
+  did: string;
+  role: MemberRole;
+}
+
+export interface Repo {
+  type: "logicsrc.repo";
+  version: string;
+  name: string;
+  slug: string;
+  description?: string;
+  owner_did: string;
+  board?: string;
+  visibility: Visibility;
+  default_branch: string;
+  backend: {
+    provider: "forgejo" | "github" | "git";
+    url: string;
+    external_id?: string;
+  };
+  members: RepoMember[];
+  merge_policy: MergePolicy;
+  created_at?: string;
+}
+
+export interface Review {
+  reviewer_did: string;
+  decision: ReviewDecision;
+  reputation?: number;
+  summary?: string;
+  created_at?: string;
+}
+
+export interface Check {
+  name: string;
+  status: CheckStatus;
+  url?: string;
+}
+
+export interface PullRequest {
+  type: "logicsrc.pull_request";
+  version: string;
+  repo: string;
+  number?: number;
+  title: string;
+  description?: string;
+  author_did: string;
+  source_branch: string;
+  target_branch: string;
+  head_sha?: string;
+  task?: string;
+  status: PullRequestStatus;
+  checks: Check[];
+  reviews: Review[];
+  merge?: {
+    method: MergeMethod;
+    merged_by_did: string;
+    merge_sha?: string;
+    policy_satisfied: boolean;
+    merged_at?: string;
+  };
+  created_at?: string;
+  updated_at?: string;
+}