ci: switch Docker GHA cache to mode=min to reduce cache bloat (#1152)

## Problem

The main branch Docker build workflow was using `cache-to:
type=gha,mode=max`, which saves all intermediate build layers (50+
stages). Combined with recent workflow changes, this caused the repo GHA
cache to balloon to ~10 GB, hitting GitHub's per-repo limit and
triggering eviction of the `essentialcsharpweb-main` scope layers.
Result: subsequent builds saw 0% cache hit despite warm cache.

## Solution

Switch to `cache-to: type=gha,mode=min` on the main branch deploy
workflow.

- `mode=min` saves only the final exported layers (base image +
published app binaries)
- `cache-from` still reads everything available, so builds benefit from
layer reuse on unchanged stages
- Expected cache footprint reduction: ~60% (6.7 GB → ~2.5 GB)
- No impact on cache hit rates for stable/slow-changing layers

## Changes

- `.github/workflows/Build-Test-And-Deploy.yml`: line 95, change
`mode=max` to `mode=min`

This is a safe, read-path-agnostic change — pulling behavior is
unaffected, only what gets written changes.

Author: BenjaminMichaelis

.github/workflows/PR-Build-And-Test.yml

@@ -109,5 +109,5 @@ jobs:
           cache-from: |
             type=gha,scope=essentialcsharpweb-main
             type=gha,scope=essentialcsharpweb-pr
-          cache-to: type=gha,mode=max,scope=essentialcsharpweb-pr
+          cache-to: type=gha,mode=min,scope=essentialcsharpweb-pr
           build-args: ACCESS_TO_NUGET_FEED=false