feat: expand API documentation for repository settings and GitHub Actions management

contracts/gitea-api.md

@@ -453,22 +453,146 @@ Auth: `Authorization: token ${GITHUB_TOKEN}`
 
 ### PATCH /repos/{owner}/{repo}
 
-**Used in**: Phase 8 (archive repos + update description), Phase 8 teardown (un-archive)
+**Used in**: Phase 8 (mark as mirror + update description), Phase 8 teardown (restore settings)
 **Purpose**: Update repository settings
 
-**Request (archive)**:
+**Request (mark as mirror)**:
 ```json
 {
-  "archived": true,
+  "description": "[MIRROR] Offsite backup — primary at https://git.domain.com/org/repo — was: original description",
-  "description": "[MOVED] Now at https://git.domain.com/org/repo — was: original description"
+  "homepage": "https://git.domain.com/org/repo",
+  "has_wiki": false,
+  "has_projects": false
 }
 ```
 
-**Request (un-archive)**:
+**Request (restore)**:
 ```json
 {
-  "archived": false
+  "description": "original description",
+  "homepage": "original homepage",
+  "has_wiki": true,
+  "has_projects": true
 }
 ```
 
 **Response** (200): Updated repository object
+
+### PUT /repos/{owner}/{repo}/actions/permissions
+
+**Used in**: Phase 6 (disable Actions), Phase 6 teardown (re-enable)
+**Purpose**: Enable or disable GitHub Actions on a repo
+
+**Request**:
+```json
+{
+  "enabled": false
+}
+```
+
+**Response** (204): No Content
+
+### GET /repos/{owner}/{repo}/pages
+
+**Used in**: Phase 8 (snapshot Pages state for teardown)
+**Purpose**: Get GitHub Pages configuration
+
+**Response** (200):
+```json
+{
+  "cname": "string",
+  "source": {
+    "branch": "main",
+    "path": "/"
+  }
+}
+```
+
+**404**: Pages not enabled for this repo
+
+### DELETE /repos/{owner}/{repo}/pages
+
+**Used in**: Phase 8 (disable Pages on mirror)
+**Purpose**: Disable GitHub Pages
+
+**Response** (204): No Content
+
+---
+
+## Error Responses
+
+All Gitea and GitHub API endpoints return standard HTTP error codes. The migration
+scripts check `http_code >= 400` in `_api_call()` (lib/common.sh) and treat any
+4xx/5xx as a failure.
+
+### Common Error Codes
+
+| Code | Meaning | Typical Cause |
+|------|---------|---------------|
+| 400 | Bad Request | Malformed JSON, missing required fields, invalid field values |
+| 401 | Unauthorized | Token expired, revoked, or missing |
+| 403 | Forbidden | Token lacks required scope (e.g., admin endpoint with non-admin token) |
+| 404 | Not Found | Resource doesn't exist — used for idempotency checks (`GET` before `POST`) |
+| 409 | Conflict | Resource already exists (e.g., duplicate token name, duplicate org name) |
+| 422 | Unprocessable Entity | Validation failed (e.g., password too short, invalid repo name) |
+| 500 | Internal Server Error | Server-side failure — retry may work for transient issues |
+
+### Error Response Body
+
+Gitea errors return JSON with a `message` field:
+```json
+{
+  "message": "string describing the error",
+  "url": "https://gitea.docs/api/endpoint"
+}
+```
+
+GitHub errors return JSON with `message` and optionally `errors`:
+```json
+{
+  "message": "Validation Failed",
+  "errors": [
+    {
+      "resource": "Repository",
+      "field": "name",
+      "code": "already_exists"
+    }
+  ]
+}
+```
+
+### How Scripts Handle Errors
+
+- `_api_call()` logs the full response body on any 4xx/5xx and returns exit code 1
+- Callers either `exit 1` (fatal) or continue with `|| true` (non-fatal, e.g., sync triggers)
+- Idempotency checks use 404 as a signal to proceed with creation — this is expected, not an error
+
+---
+
+## Pagination
+
+Gitea list endpoints return paginated results. The migration scripts do NOT
+paginate because the data volumes are small (3 repos, ~3 runners, ~3 mirrors).
+
+### Gitea Pagination Headers
+
+```
+x-total-count: 42
+link: <url?page=2&limit=50>; rel="next", <url?page=5&limit=50>; rel="last"
+```
+
+### Default Limits
+
+| Endpoint | Default per-page | Max per-page |
+|----------|:----------------:|:------------:|
+| GET /admin/runners | 50 | 50 |
+| GET /repos/{owner}/{repo}/push_mirrors | 50 | 50 |
+| GET /repos/{owner}/{repo}/commits | 50 | 50 |
+| GET /repos/{owner}/{repo}/branch_protections | all (no pagination) | — |
+
+### When Pagination Would Matter
+
+If any of these grow beyond 50 items, scripts that use these endpoints would
+silently miss results. For this migration (3 repos, handful of runners), this
+is not a concern. If extending to N repos where N > 50, add `?limit=N` or
+implement `Link` header following.