Cut per-request origin work: batched article loads, no session write per page

The origin was 3–8 ms per page, almost all of it per-statement overhead:
an issue page ran two statements per pick (~55 on a 25-article issue) and
every signed-in page wrote its session row back because `take_flash`
called `Session::remove`, which marks the session modified even when the
key is absent.

- `Db::get_articles` loads an issue's articles and their social rows in
  two statements; both branches of `web::issue::load` use it. The
  single-id and batch queries share one projection via a macro.
- `take_flash` reads before removing, and touches a signed-in session at
  most once a day so the inactivity expiry still slides. Anonymous
  requests never create a session.
- `Server-Timing: app;dur=<ms>` on every response, outermost layer.
- `reject_early_data`: 425 for a non-safe method that arrived as TLS 0-RTT
  data, so nginx `ssl_early_data on` is safe (RFC 8470 §5.2).
- `[profile.release]`: fat LTO, one codegen unit (binary 46 → 29 MB).

Docs: the Cloudflare proxy was retired on 2026-09-05 after measuring
+43 ms per signed-in page from Boston; README reverse-proxy section is
now the direct setup (upstream keepalive, 0-RTT lines) and the CDN
runbook carries a retired-status banner.

Dev seed, app-side: `/` 21 → 5 statements, 3.7 → 1.0 ms; `/feed.xml`
44 → 12, 9.1 → 3.0 ms; session writes per signed-in page 1 → 0.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Va5eMEmWEnjMXBsBob5FDW

src/server.rs

@@ -182,7 +182,9 @@ pub fn router(state: AppState) -> Router {
             state.clone(),
             crate::web::session::require_same_origin,
         ))
+        .layer(from_fn(crate::web::reject_early_data))
         .layer(from_fn(crate::web::security_headers))
+        .layer(from_fn(crate::web::server_timing))
         .with_state(state)
 }