fix: bump Go image to 1.26 to match go.mod requirement

go.mod declares go 1.26.1; docker build was failing with
"go.mod requires go >= 1.26.1 (running go 1.22.12; GOTOOLCHAIN=local)"

- Dockerfile: golang:1.22-alpine → golang:1.26-alpine
- .woodpecker.yml: test image 1.22-alpine → 1.26-alpine;
  gosec image 1.22-bookworm → 1.26-bookworm
- CLAUDE.md: update stack note to Go 1.26+

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.woodpecker.yml

@@ -5,7 +5,7 @@ steps:
       - golangci-lint run ./...
 
   - name: test
-    image: golang:1.22-alpine
+    image: golang:1.26-alpine
     commands:
       - go test ./...
 
@@ -23,7 +23,7 @@ steps:
       - event: [push, pull_request]
 
   - name: gosec
-    image: golang:1.22-bookworm
+    image: golang:1.26-bookworm
     commands:
       - go install github.com/securego/gosec/v2/cmd/gosec@latest
       - gosec -exclude=G120,G706,G101,G115,G203,G124 ./...

CLAUDE.md

@@ -6,7 +6,7 @@
 
 ## Stack
 
-- **Language:** Go 1.22+
+- **Language:** Go 1.26+
 - **HTTP:** `net/http` (stdlib) + `chi` router (lightweight)
 - **Database:** MongoDB (OAuth token storage)
 - **Mongo driver:** `go.mongodb.org/mongo-driver/v2`

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.22-alpine AS builder
+FROM golang:1.26-alpine AS builder
 WORKDIR /app
 COPY go.mod go.sum ./
 RUN go mod download