Consolidate tools from 110 to 45 using method dispatch (#143)

Consolidate 110 individual MCP tools down to 45 using a method dispatch pattern, aligning tool names with the GitHub MCP server conventions.

**Motivation:** LLMs work better with fewer, well-organized tools. The method dispatch pattern (used by GitHub's MCP server) groups related operations under read/write tools with a `method` parameter.

**Changes:**
- Group related tools into `_read`/`_write` pairs with method dispatch (e.g. `issue_read`, `issue_write`, `pull_request_read`, `pull_request_write`)
- Rename tools to match GitHub MCP naming (`get_file_contents`, `create_or_update_file`, `list_issues`, `list_pull_requests`, etc.)
- Rename `pageSize` to `perPage` for GitHub MCP compat
- Move issue label ops (`add_labels`, `remove_label`, etc.) into `issue_write`
- Merge `create_file`/`update_file` into `create_or_update_file` with optional `sha`
- Make `delete_file` require `sha`
- Add `get_labels` method to `issue_read`
- Add shared helpers: `GetInt64Slice`, `GetStringSlice`, `GetPagination` in params package
- Unexport all dispatch handler functions
- Fix: pass assignees/milestone in `CreateIssue`, bounds check in `GetFileContent`

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/143
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

operation/repo/tag.go

@@ -54,7 +54,7 @@ var (
 		mcp.WithString("owner", mcp.Required(), mcp.Description("repository owner")),
 		mcp.WithString("repo", mcp.Required(), mcp.Description("repository name")),
 		mcp.WithNumber("page", mcp.Description("page number"), mcp.DefaultNumber(1), mcp.Min(1)),
-		mcp.WithNumber("pageSize", mcp.Description("page size"), mcp.DefaultNumber(20), mcp.Min(1)),
+		mcp.WithNumber("perPage", mcp.Description("results per page"), mcp.DefaultNumber(20), mcp.Min(1)),
 	)
 )
 
@@ -179,7 +179,7 @@ func ListTagsFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResu
 		return to.ErrorResult(err)
 	}
 	page := params.GetOptionalInt(args, "page", 1)
-	pageSize := params.GetOptionalInt(args, "pageSize", 20)
+	pageSize := params.GetOptionalInt(args, "perPage", 20)
 
 	client, err := gitea.ClientFromContext(ctx)
 	if err != nil {