feat: add PR/release/branch/milestone/comment write tools

Adds six opt-in write tools (write-mode + policy + per-user permission still
enforced; no destructive or admin actions):

- create_pull_request (POST /pulls)
- create_release / edit_release (POST/PATCH /releases)
- create_branch (POST /branches; create only, no deletion)
- create_milestone (POST /milestones)
- edit_issue_comment (PATCH /issues/comments/{id})

Each: arg schema (extra=forbid, GitRef on branch/ref-like fields), Gitea client
method with url-encoded path segments, handler that surfaces auth errors, MCP
registration (write_operation=True), server wiring, docs, and success tests.

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

src/aegis_gitea_mcp/server.py

@@ -81,10 +81,16 @@ from aegis_gitea_mcp.tools.repository import (
 from aegis_gitea_mcp.tools.write_tools import (
     add_labels_tool,
     assign_issue_tool,
+    create_branch_tool,
     create_issue_comment_tool,
     create_issue_tool,
     create_label_tool,
+    create_milestone_tool,
     create_pr_comment_tool,
+    create_pull_request_tool,
+    create_release_tool,
+    edit_issue_comment_tool,
+    edit_release_tool,
     remove_labels_tool,
     update_issue_tool,
     update_label_tool,
@@ -348,6 +354,12 @@ TOOL_HANDLERS: dict[str, ToolHandler] = {
     "create_label": create_label_tool,
     "update_label": update_label_tool,
     "remove_labels": remove_labels_tool,
+    "create_pull_request": create_pull_request_tool,
+    "create_release": create_release_tool,
+    "edit_release": edit_release_tool,
+    "create_branch": create_branch_tool,
+    "create_milestone": create_milestone_tool,
+    "edit_issue_comment": edit_issue_comment_tool,
 }