docker: drop runtime PHP scan-dir discovery for env var + apk path glob

The previous build-time discovery via PHP_CONFIG_FILE_SCAN_DIR worked
but invoked a PHP binary just to learn a path that's already a stable
contract of each base image:

* php:8-apache exports PHP_INI_DIR=/usr/local/etc/php as part of the
  docker-library image template, stable across PHP majors. Reference
  it directly in the COPY destination — no RUN, no validation needed.

* Alpine's apk php-apache2 always installs mod_php's conf.d at
  /etc/phpXX/conf.d (currently /etc/php84). The FROM php:8-alpine
  image also ships its own PHP at /usr/local/etc/php/conf.d, but
  mod_php doesn't read from there. Glob /etc/php*/conf.d to track
  the apk-installed PHP major automatically; explicit error if the
  glob matches nothing.

Net effect: Debian goes from a 5-line RUN block to a 1-line COPY.
Alpine keeps a small RUN block but no longer invokes a PHP binary,
so it doesn't matter which of the two PHP installs `php` resolves
to via $PATH.

Verified: both variants build, install the override at the right
conf.d, mod_php reports post_max_size=32M, and a 20 MB POST to
/backend/empty.php returns HTTP 200 / 0 bytes with no warnings.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -10,11 +10,10 @@ RUN install-php-extensions iconv gd pdo pdo_mysql pdo_pgsql pgsql \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
-COPY docker/librespeed-php.ini /tmp/librespeed-php.ini
-RUN scan_dir="$(php -r 'echo rtrim(PHP_CONFIG_FILE_SCAN_DIR);')" \
-    && [ -n "$scan_dir" ] \
-    && install -D -m 0644 /tmp/librespeed-php.ini "$scan_dir/99-librespeed.ini" \
-    && rm /tmp/librespeed-php.ini
+# PHP_INI_DIR is set by the official php:8-apache image to /usr/local/etc/php
+# and has been stable across PHP majors. Using the env var documents intent
+# and follows any future upstream change to the path automatically.
+COPY docker/librespeed-php.ini ${PHP_INI_DIR}/conf.d/99-librespeed.ini
 
 # Prepare files and folders
 RUN mkdir -p /speedtest/

Dockerfile.alpine

@@ -20,11 +20,22 @@ RUN apk add --quiet --no-cache \
 RUN ln -sf /dev/stdout /var/log/apache2/access.log && \
     ln -sf /dev/stderr /var/log/apache2/error.log
 
+# This image has two PHP installs: the FROM php:8-alpine binary (conf.d at
+# /usr/local/etc/php/conf.d) and the apk-installed php-apache2 (conf.d at
+# /etc/phpXX/conf.d). mod_php uses the apk one — glob /etc/php*/conf.d to
+# find it without pinning the PHP major.
 COPY docker/librespeed-php.ini /tmp/librespeed-php.ini
-RUN scan_dir="$(/usr/bin/php -r 'echo rtrim(PHP_CONFIG_FILE_SCAN_DIR);')" \
-    && [ -n "$scan_dir" ] \
-    && install -D -m 0644 /tmp/librespeed-php.ini "$scan_dir/99-librespeed.ini" \
-    && rm /tmp/librespeed-php.ini
+RUN set -eu; \
+    scan_dir=""; \
+    for d in /etc/php*/conf.d; do \
+      [ -d "$d" ] && scan_dir="$d" && break; \
+    done; \
+    if [ -z "$scan_dir" ]; then \
+      echo "ERROR: no /etc/php*/conf.d directory found; apk php-apache2 install layout may have changed" >&2; \
+      exit 1; \
+    fi; \
+    install -D -m 0644 /tmp/librespeed-php.ini "$scan_dir/99-librespeed.ini"; \
+    rm /tmp/librespeed-php.ini
 
 # Prepare files and folders
 RUN mkdir -p /speedtest/