v0.35.1: performance, AGPL licensing and documentation overhaul

- Web Server reads static files inline; proxy middleware chain flattened
- About window with license summary and project links; AGPL-3.0-or-later
- Rewritten documentation: feature list, screenshots, performance guide
- Fix false spikes in per-Vhost request-rate charts

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMsgSXoK4Bph2vU6fSBkAH

src/cache/policy/response.rs

@@ -61,9 +61,9 @@ pub fn plan(
         return None;
     }
     if status != StatusCode::OK
-        || headers.contains_key("set-cookie")
-        || headers.contains_key("content-range")
-        || headers.contains_key("trailer")
+        || headers.contains_key(::http::header::SET_COOKIE)
+        || headers.contains_key(::http::header::CONTENT_RANGE)
+        || headers.contains_key(::http::header::TRAILER)
     {
         return None;
     }
@@ -75,7 +75,7 @@ pub fn plan(
         return None;
     }
     if headers
-        .get("content-type")
+        .get(::http::header::CONTENT_TYPE)
         .and_then(|v| v.to_str().ok())
         .is_some_and(|v| {
             let v = v.trim_start().to_ascii_lowercase();
@@ -92,14 +92,11 @@ pub fn plan(
     {
         return None;
     }
-    // Surrogate-Control: no-store is a shared-cache veto in compatibility
-    // mode, regardless of public/fallback TTL or any other directive.
+    // Surrogate-Control: no-store always vetoes shared caching.
     if settings.varnish_compatible && surrogate_no_store(headers) {
         return None;
     }
-    // Explicitly configured fallback TTL is an opt-in origin no-cache
-    // override *only* for public responses. With fallback disabled, keep
-    // the pre-0.34.7 validator-based revalidation and never grant a HIT.
+    // Fallback TTL overrides origin no-cache only for public responses.
     let override_public_no_cache = settings.varnish_compatible
         && control.contains_key("no-cache")
         && control.contains_key("public")
@@ -117,13 +114,13 @@ pub fn plan(
     let mut stale_while_revalidate = parse_window("stale-while-revalidate")?;
     let stale_if_error = parse_window("stale-if-error")?;
     if requires_revalidation
-        && !headers.contains_key("etag")
-        && !headers.contains_key("last-modified")
+        && !headers.contains_key(::http::header::ETAG)
+        && !headers.contains_key(::http::header::LAST_MODIFIED)
     {
         return None;
     }
     let now = SystemTime::now();
-    let date = match headers.get("date") {
+    let date = match headers.get(::http::header::DATE) {
         Some(v) => httpdate::parse_http_date(v.to_str().ok()?).ok()?,
         None => now,
     };
@@ -131,7 +128,7 @@ pub fn plan(
         Some(settings.default_ttl_seconds)
     } else if let Some(value) = control.get("s-maxage").or_else(|| control.get("max-age")) {
         Some(value.as_ref()?.parse::<u64>().ok()?)
-    } else if let Some(expires) = headers.get("expires") {
+    } else if let Some(expires) = headers.get(::http::header::EXPIRES) {
         Some(
             httpdate::parse_http_date(expires.to_str().ok()?)
                 .ok()?
@@ -144,7 +141,7 @@ pub fn plan(
     } else {
         None
     };
-    let age = match headers.get("age") {
+    let age = match headers.get(::http::header::AGE) {
         Some(v) => v.to_str().ok()?.parse::<u64>().ok()?,
         None => 0,
     };
@@ -161,11 +158,7 @@ pub fn plan(
         None if requires_revalidation => 0,
         None => return None,
     };
-    // Retain zero-TTL and already-expired representations for conditional
-    // revalidation, client max-stale or stale-if-error. They must not be
-    // served as fresh HITs. Varnish-style grace is only implicit when the
-    // origin did not explicitly set stale-while-revalidate (including =0),
-    // the object arrived fresh and no origin no-cache rule is in effect.
+    // Expired entries are kept for revalidation only; implicit grace needs no explicit SWR/no-cache.
     if settings.varnish_compatible
         && !control.contains_key("stale-while-revalidate")
         && !control.contains_key("no-cache")
@@ -184,7 +177,7 @@ pub fn plan(
     {
         return None;
     }
-    let expected_length = match headers.get("content-length") {
+    let expected_length = match headers.get(::http::header::CONTENT_LENGTH) {
         Some(v) => Some(v.to_str().ok()?.parse::<usize>().ok()?),
         None => None,
     };