chore: add golangci-lint, bump Go to 1.26, fix all lint issues (#133)

## Summary
- Add `.golangci.yml` with linter configuration matching the main gitea repo
- Add `lint`, `lint-fix`, `lint-go`, `lint-go-fix`, and `security-check` Makefile targets
- Add `tidy` Makefile target (extracts min Go version from `go.mod` for `-compat` flag)
- Bump minimum Go version to 1.26
- Update golangci-lint to v2.10.1
- Replace `golang/govulncheck-action` with `make security-check` in CI
- Add `make lint` step to CI
- Fix all lint issues across the codebase (formatting, `errors.New` vs `fmt.Errorf`, `any` vs `interface{}`, unused returns, stuttering names, Go 1.26 `new(expr)`, etc.)
- Remove unused `pkg/ptr` package (inlined by Go 1.26 `new(expr)`)
- Remove dead linter exclusions (staticcheck, gocritic, testifylint, dupl)

## Test plan
- [x] `make lint` passes
- [x] `go test ./...` passes
- [x] `make build` succeeds

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/133
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/params/params_test.go

@@ -8,7 +8,7 @@ import (
 func TestGetIndex(t *testing.T) {
 	tests := []struct {
 		name      string
-		args      map[string]interface{}
+		args      map[string]any
 		key       string
 		wantIndex int64
 		wantErr   bool
@@ -16,63 +16,63 @@ func TestGetIndex(t *testing.T) {
 	}{
 		{
 			name:      "valid float64",
-			args:      map[string]interface{}{"index": float64(123)},
+			args:      map[string]any{"index": float64(123)},
 			key:       "index",
 			wantIndex: 123,
 			wantErr:   false,
 		},
 		{
 			name:      "valid string",
-			args:      map[string]interface{}{"index": "456"},
+			args:      map[string]any{"index": "456"},
 			key:       "index",
 			wantIndex: 456,
 			wantErr:   false,
 		},
 		{
 			name:      "valid string with large number",
-			args:      map[string]interface{}{"index": "999999"},
+			args:      map[string]any{"index": "999999"},
 			key:       "index",
 			wantIndex: 999999,
 			wantErr:   false,
 		},
 		{
 			name:    "missing parameter",
-			args:    map[string]interface{}{},
+			args:    map[string]any{},
 			key:     "index",
 			wantErr: true,
 			errMsg:  "index is required",
 		},
 		{
 			name:    "invalid string (not a number)",
-			args:    map[string]interface{}{"index": "abc"},
+			args:    map[string]any{"index": "abc"},
 			key:     "index",
 			wantErr: true,
 			errMsg:  "must be a valid integer",
 		},
 		{
 			name:    "invalid string (decimal)",
-			args:    map[string]interface{}{"index": "12.34"},
+			args:    map[string]any{"index": "12.34"},
 			key:     "index",
 			wantErr: true,
 			errMsg:  "must be a valid integer",
 		},
 		{
 			name:    "invalid type (bool)",
-			args:    map[string]interface{}{"index": true},
+			args:    map[string]any{"index": true},
 			key:     "index",
 			wantErr: true,
 			errMsg:  "must be a number or numeric string",
 		},
 		{
 			name:    "invalid type (map)",
-			args:    map[string]interface{}{"index": map[string]string{"foo": "bar"}},
+			args:    map[string]any{"index": map[string]string{"foo": "bar"}},
 			key:     "index",
 			wantErr: true,
 			errMsg:  "must be a number or numeric string",
 		},
 		{
 			name:      "custom key name",
-			args:      map[string]interface{}{"pr_index": "789"},
+			args:      map[string]any{"pr_index": "789"},
 			key:       "pr_index",
 			wantIndex: 789,
 			wantErr:   false,