share: dockerize the file-share pipeline and document it

The Python half of the short-lived share links lived in the repo; the Apache
config and the cron entries that make it work were hand-placed on the host, so
the feature could not be rebuilt from a checkout. This adds the missing half.

Scripts (defaults unchanged, so existing bare-metal cron keeps working):
* scan_shares.py / revoke_shares.py take their paths from CONJURER_SHARE_*
  instead of hardcoding the Pi layout, and create their parent dirs;
* the revoke TTL is now CONJURER_SHARE_TTL_SECONDS. Its --help claimed "2min"
  while the code used a hardcoded 3600 - the help text now reports the real,
  configured value.

New share service:
* docker/Dockerfile.share - Apache + the two jobs, reusing the same scripts
  rather than forking copies;
* docker/share-vhost.conf.tpl - the previously undocumented Apache half.
  Three settings are load-bearing and commented as such: +FollowSymLinks (the
  shares ARE symlinks), -Indexes (a listing would expose every live token), and
  a deny rule for dotfiles (revoke_shares.py keeps .downloads.json - a map of
  every live token - inside the served directory);
* docker/entrypoint.share.sh - renders the vhost, seeds the index on first run,
  then runs scanner/revoker in sleep loops beside Apache (no cron, so their
  output shows up in docker logs);
* compose + env example, incl. the two volumes that MUST be shared with the
  musician (it creates the links and reads the index).

docs/deployment/FILE_SHARING.md documents the mechanism, both deployment routes
(docker and existing host Apache), the Discord command, why each Apache setting
matters, verification commands, and the known limitations - notably that a link
nobody ever downloads is never revoked, since the TTL starts at first download.

Verified: scanner and revoker exercised end-to-end against temp dirs (index
built; token recorded from a combined-format log line and the symlink unlinked).
Compose file not validated - no docker on this machine.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/entrypoint.share.sh

@@ -0,0 +1,67 @@
+#!/bin/sh
+# Entrypoint for the Conjurer share container: renders the vhost, seeds the
+# share index, then runs the two periodic jobs alongside Apache.
+#
+# Cron is deliberately not used. Both scripts are already written to be safe to
+# re-run (the scanner writes atomically, the revoker persists its log position),
+# so plain sleep loops give the same result with one less moving part and with
+# their output on the container's stdout where `docker logs` can see it.
+set -eu
+
+: "${CONJURER_SHARE_SERVER_NAME:=localhost}"
+: "${CONJURER_SHARE_SCAN_PATH:=/mnt/shares}"
+: "${CONJURER_SHARE_DB:=/srv/share/db/share_scan.json}"
+: "${CONJURER_SHARE_DIR:=/var/www/html/share}"
+: "${CONJURER_APACHE_LOG:=/var/log/apache2/share_access.log}"
+: "${CONJURER_SHARE_SCAN_INTERVAL:=3600}"
+: "${CONJURER_SHARE_REVOKE_INTERVAL:=60}"
+: "${CONJURER_SHARE_TTL_SECONDS:=3600}"
+export CONJURER_SHARE_SCAN_PATH CONJURER_SHARE_DB CONJURER_SHARE_DIR \
+       CONJURER_APACHE_LOG CONJURER_SHARE_TTL_SECONDS
+
+# Render the vhost (same placeholder pattern as icecast.xml.tpl).
+sed "s|__SERVER_NAME__|${CONJURER_SHARE_SERVER_NAME}|g" \
+    /app/share-vhost.conf.tpl > /etc/apache2/sites-available/000-default.conf
+
+mkdir -p "$CONJURER_SHARE_DIR" \
+         "$(dirname "$CONJURER_SHARE_DB")" \
+         "$(dirname "$CONJURER_APACHE_LOG")" \
+         /var/run/apache2
+chown -R www-data:www-data "$CONJURER_SHARE_DIR"
+
+# revoke_shares.py seeks to a stored byte offset, so the log must exist before
+# the first pass or it starts by reporting an error.
+touch "$CONJURER_APACHE_LOG"
+
+# Seed the index immediately when absent - otherwise /get_share_list returns
+# nothing until the first scheduled scan, which looks like a broken feature.
+if [ ! -f "$CONJURER_SHARE_DB" ]; then
+    echo "[share] no index at $CONJURER_SHARE_DB - running initial scan of $CONJURER_SHARE_SCAN_PATH"
+    python3 /app/scan_shares.py || echo "[share] initial scan failed, continuing"
+fi
+
+# Periodic index rebuild.
+(
+    while true; do
+        sleep "$CONJURER_SHARE_SCAN_INTERVAL"
+        echo "[share] rescanning $CONJURER_SHARE_SCAN_PATH"
+        python3 /app/scan_shares.py || echo "[share] scan failed"
+    done
+) &
+SCAN_PID=$!
+
+# Periodic revocation of links whose TTL expired after first download.
+(
+    while true; do
+        sleep "$CONJURER_SHARE_REVOKE_INTERVAL"
+        python3 /app/revoke_shares.py || echo "[share] revoke failed"
+    done
+) &
+REVOKE_PID=$!
+
+trap 'kill "$SCAN_PID" "$REVOKE_PID" 2>/dev/null || true' INT TERM
+
+echo "[share] serving $CONJURER_SHARE_DIR as ${CONJURER_SHARE_SERVER_NAME}/share"
+echo "[share] scan every ${CONJURER_SHARE_SCAN_INTERVAL}s, revoke sweep every ${CONJURER_SHARE_REVOKE_INTERVAL}s, TTL ${CONJURER_SHARE_TTL_SECONDS}s after first download"
+
+exec apache2ctl -D FOREGROUND