Add missing tool parameters from Gitea SDK (#164)

Expose additional parameters that the Gitea SDK supports but were not yet wired through the MCP tool definitions.

**Motivation:** Systematic comparison against github-mcp-server and the Gitea SDK revealed several supported parameters that were missing from tool schemas.

- `list_issues`: `labels`, `since`, `before` filters
- `issue_write`: `labels` and `deadline` on create, `deadline`/`remove_deadline` on update
- `pull_request_write`: `labels`/`deadline` on create/update, `remove_deadline` on update, `force_merge`/`merge_when_checks_succeed`/`head_commit_id` on merge
- `list_branches`: `page`/`perPage` pagination
- `create_repo`: `trust_model`, `object_format_name`
- `label_write`: `is_archived` on create/edit

**Testing:** Added tests for issue list filters, issue create labels/deadline, PR create labels/deadline, and PR merge new params.

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/164
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/params/params.go

@@ -3,6 +3,7 @@ package params
 import (
 	"fmt"
 	"strconv"
+	"time"
 )
 
 // GetString extracts a required string parameter from MCP tool arguments.
@@ -101,6 +102,18 @@ func GetInt64Slice(args map[string]any, key string) ([]int64, error) {
 	return out, nil
 }
 
+// GetOptionalTime extracts an optional RFC3339 timestamp parameter, returning nil if missing or unparseable.
+func GetOptionalTime(args map[string]any, key string) *time.Time {
+	val, ok := args[key].(string)
+	if !ok {
+		return nil
+	}
+	if t, err := time.Parse(time.RFC3339, val); err == nil {
+		return &t
+	}
+	return nil
+}
+
 // GetOptionalInt extracts an optional integer parameter from MCP tool arguments.
 // Returns defaultVal if the key is missing or the value cannot be parsed.
 // Accepts both float64 (JSON number) and string representations.