deps(docker): bump golang from 1.24.6-alpine to 1.25.6-alpine

Bumps golang from 1.24.6-alpine to 1.25.6-alpine.

---
updated-dependencies:
- dependency-name: golang
  dependency-version: 1.25.6-alpine
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Dockerfile

@@ -16,7 +16,7 @@ COPY frontend/ ./
 RUN npm run build
 
 # Stage 2: Build Go binary
-FROM golang:1.25.7-alpine AS builder
+FROM golang:1.26rc3-alpine AS builder
 
 # Install build dependencies (no gcc/musl-dev needed - pure Go SQLite driver)
 RUN apk add --no-cache git tzdata