feat: merge oo-cli and extend library with Calendar/CRM/subtasks/files

- Add Calendar helpers (ListCalendars/ListEvents/AddEvent/DeleteEvent)
- Add CRM helpers: contacts, opportunities, cases, CRM tasks, history notes
- Add project-task extras (ListTasks/ListAllTasks/GetTaskByID/AddTask/
  AddSubtask/UpdateTaskStatus/DeleteTask, GetProjectByID)
- Add UploadOpportunityFile (multipart) and SelfUserID caching
- Introduce Defaults struct, SetDefaults, GetEnvironmentDefaults;
  GetEnvironmentCredentials now accepts ONLYOFFICE_HOST/NAME/PASSWORD aliases
- Add public Authenticate() helper that eagerly primes the token
- Bundle Cobra CLI at cmd/oo-cli with full command surface
  (calendar, tasks, subtasks, CRM, applications-sync); CLI-only deps
  (cobra, godotenv) kept out of the library surface
- Add httptest-based unit tests for form/multipart helpers
- Docs: CHANGELOG, AGENTS, .env.example, README updates for v0.3 features

Consolidates the standalone eSlider/oo-cli tool into this canonical Go
module (see eSlider/inventar ASR-0008).

Made-with: Cursor

files.go

@@ -0,0 +1,27 @@
+package onlyoffice
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/url"
+)
+
+// UploadOpportunityFile uploads a single file to a CRM opportunity.
+// Returns the decoded "response" object from OnlyOffice.
+func (c *Client) UploadOpportunityFile(ctx context.Context, opportunityID, filePath string) (map[string]any, error) {
+	path := fmt.Sprintf("/api/2.0/crm/opportunity/%s/files/upload.json", url.PathEscape(opportunityID))
+	raw, err := c.uploadMultipart(ctx, path, "file", filePath)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := responseField(raw, "response")
+	if err != nil {
+		return nil, err
+	}
+	var out map[string]any
+	if err := json.Unmarshal(resp, &out); err != nil {
+		return nil, err
+	}
+	return out, nil
+}