docs(remote): document the wake-on-LAN invariants; drop wake state on bulk delete

Self-review pass: the input-ladder's two 'buffer' branches were the same three
lines, and bulk delete left a session's (bounded, per-random-uuid) wake state
behind. Documents the design where the code refers to it - remote-sessions.md
section, the architecture invariant, and the CLAUDE.md key pattern.

src/web/routes/session-routes.ts

@@ -1322,6 +1322,7 @@ export function registerSessionRoutes(
 
     for (const id of sessionIds) {
       if (ctx.sessions.has(id)) {
+        remoteWake.drop(id);
         await ctx.cleanupSession(id, true, 'user_bulk_delete');
         killed++;
       }