fix(review-2): medium/low + docs — config validation, hygiene, doc sync

- compression_concurrency wired to boot config (state.rs) and removed as a
  dead admin control.
- patch_config gains per-key integer/range validation so numerically-valid-but-
  nonsensical values (-1/NaN/3.5) are rejected instead of silently reverting to
  default at read time.
- clearAuth now also clears the display name (shared-device residual).
- e2e/Caddyfile.test mirrors prod security headers + the SSE encode-exclusion so
  the test stack is representative and can catch header regressions.
- .gitignore: ignore root-level Playwright artifacts (test-results/, report).
- docs: USER_JOURNEYS §10 and SECURITY-BACKLOG updated to match the implemented
  read-only-ban behavior and the export-path fix.

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

backend/src/handlers/admin.rs

@@ -121,15 +121,18 @@ pub async fn patch_config(
     // Numeric keys validated as f64; boolean keys validated as truthy strings; the
     // privacy note is free text. Splitting these explicitly is verbose but makes the
     // failure mode for typos obvious (`Unbekannter Schlüssel: ...`).
-    const NUMERIC_KEYS: &[&str] = &[
-        "max_image_size_mb",
-        "max_video_size_mb",
-        "upload_rate_per_hour",
-        "feed_rate_per_min",
-        "export_rate_per_day",
-        "quota_tolerance",
-        "estimated_guest_count",
-        "compression_concurrency",
+    // (key, integer_only, min, max). Ranges reject values that `parse::<f64>` would
+    // accept but that silently revert to the hardcoded default at read time
+    // (get_usize/get_i64 can't parse negatives/NaN/fractionals). `compression_concurrency`
+    // is intentionally absent — it's read once at boot, so a live edit was a no-op.
+    const NUMERIC_SPECS: &[(&str, bool, f64, f64)] = &[
+        ("max_image_size_mb", true, 1.0, 1024.0),
+        ("max_video_size_mb", true, 1.0, 10240.0),
+        ("upload_rate_per_hour", true, 1.0, 100_000.0),
+        ("feed_rate_per_min", true, 1.0, 100_000.0),
+        ("export_rate_per_day", true, 1.0, 100_000.0),
+        ("quota_tolerance", false, 0.0, 1.0),
+        ("estimated_guest_count", true, 1.0, 1_000_000.0),
     ];
     const BOOL_KEYS: &[&str] = &[
         "rate_limits_enabled",
@@ -150,10 +153,26 @@ pub async fn patch_config(
     // update behind — validation must fully precede any write.
     for (key, value) in &body {
         let key_str = key.as_str();
-        if NUMERIC_KEYS.contains(&key_str) {
-            if value.parse::<f64>().is_err() {
+        if let Some(&(_, integer_only, min, max)) =
+            NUMERIC_SPECS.iter().find(|(k, ..)| *k == key_str)
+        {
+            let n = value.trim().parse::<f64>().ok().filter(|n| n.is_finite());
+            let n = match n {
+                Some(n) => n,
+                None => {
+                    return Err(AppError::BadRequest(format!(
+                        "Ungültiger Wert für {key}: muss eine Zahl sein."
+                    )))
+                }
+            };
+            if integer_only && n.fract() != 0.0 {
                 return Err(AppError::BadRequest(format!(
-                    "Ungültiger Wert für {key}: muss eine Zahl sein."
+                    "Ungültiger Wert für {key}: muss eine ganze Zahl sein."
+                )));
+            }
+            if n < min || n > max {
+                return Err(AppError::BadRequest(format!(
+                    "Wert für {key} liegt außerhalb des zulässigen Bereichs ({min}–{max})."
                 )));
             }
         } else if BOOL_KEYS.contains(&key_str) {
@@ -282,7 +301,7 @@ pub async fn download_zip(
         ));
     }
 
-    let path = state.config.media_path.join("exports").join("Gallery.zip");
+    let path = state.config.export_path.join("Gallery.zip");
     if !path.exists() {
         return Err(AppError::NotFound("Exportdatei nicht gefunden.".into()));
     }
@@ -308,7 +327,7 @@ pub async fn download_html(
         ));
     }
 
-    let path = state.config.media_path.join("exports").join("Memories.zip");
+    let path = state.config.export_path.join("Memories.zip");
     if !path.exists() {
         return Err(AppError::NotFound("Exportdatei nicht gefunden.".into()));
     }

backend/src/state.rs

@@ -36,8 +36,12 @@ pub struct AppState {
 impl AppState {
     pub fn new(pool: PgPool, config: AppConfig) -> Self {
         let (sse_tx, _) = broadcast::channel(256);
-        let compression =
-            CompressionWorker::new(pool.clone(), config.media_path.clone(), 2, sse_tx.clone());
+        let compression = CompressionWorker::new(
+            pool.clone(),
+            config.media_path.clone(),
+            config.compression_concurrency,
+            sse_tx.clone(),
+        );
         Self {
             pool,
             config,