Add missing tool parameters from Gitea SDK

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

- 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

Also adds params.GetOptionalTime helper for RFC3339 timestamp parsing
and tests for the most important new parameters.

Co-Authored-By: Claude (claude-opus-4-6) <noreply@anthropic.com>

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.