docs(infra): update Forgejo docs to mirror-only, remove obsolete workflows

- Remove .forgejo/workflows/ (go-services, smoke-tests) — Forgejo is
  mirror-only, no CI/CD
- Remove setup-forgejo-runner.sh — runner removed (no macOS binary)
- Update MAC_MINI_SERVER.md: document Forgejo as mirror, fix CI/CD section
- Update FIX_COLIMA_MOUNTS.md: add root cause fix note (startup.sh)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/mac-mini/setup-forgejo-runner.sh

@@ -1,49 +0,0 @@
-#!/bin/bash
-# Register Forgejo Runner on Mac Mini
-# Run after Forgejo is up and admin user exists
-set -e
-
-DOCKER="${DOCKER_CMD:-/usr/local/bin/docker}"
-FORGEJO_URL="http://localhost:3041"
-FORGEJO_PUBLIC_URL="https://git.mana.how"
-
-# Step 1: Get runner registration token from Forgejo API
-echo "=== Getting runner registration token ==="
-API_TOKEN=$(cat /Volumes/ManaData/forgejo-api-token 2>/dev/null || echo "")
-if [ -z "$API_TOKEN" ]; then
-    echo "No API token found. Generate one:"
-    echo "  $DOCKER exec --user git mana-core-forgejo forgejo admin user generate-access-token --username till --token-name runner-setup --scopes all"
-    echo "  Save to: /Volumes/ManaData/forgejo-api-token"
-    exit 1
-fi
-
-RUNNER_TOKEN=$(curl -s -X POST "$FORGEJO_URL/api/v1/user/actions/runners/registration-token" \
-    -H "Authorization: token $API_TOKEN" | python3 -c "import sys,json; print(json.load(sys.stdin)['token'])")
-
-echo "Runner token: $RUNNER_TOKEN"
-
-# Step 2: Start runner container
-echo ""
-echo "=== Starting Forgejo Runner ==="
-$DOCKER compose -f docker-compose.macmini.yml up -d forgejo-runner
-
-# Step 3: Register runner
-echo ""
-echo "=== Registering runner ==="
-sleep 5
-
-$DOCKER exec mana-core-forgejo-runner forgejo-runner register \
-    --instance "$FORGEJO_PUBLIC_URL" \
-    --token "$RUNNER_TOKEN" \
-    --name "mac-mini" \
-    --labels "ubuntu-latest:docker://node:20,go:docker://golang:1.25-alpine,docker:docker://docker:dind" \
-    --no-interactive
-
-# Step 4: Start runner daemon
-echo ""
-echo "=== Starting runner daemon ==="
-$DOCKER restart mana-core-forgejo-runner
-
-echo ""
-echo "=== Runner registered and started ==="
-echo "Check status: $FORGEJO_PUBLIC_URL/-/admin/runners"