fix(search): use canonical severity labels

Use the shared long-form severity vocabulary in the search filter and type the range as SeverityLevel values. Preserve the existing range interaction while eliminating the private label map that had drifted from case pages.

Closes #30

Author: vsolano9

components/post/SearchResults.tsx

@@ -4,20 +4,19 @@ import { useState, useEffect, useRef } from "react";
 import Link from "next/link";
 import { PostCard } from "@/components/post/PostCard";
 import { AGENTS } from "@/lib/constants/agents";
+import {
+  isSeverityLevel,
+  SEVERITY_LABELS,
+  type SeverityLevel,
+} from "@/lib/constants/severity";
 import type { Post } from "@/types";
 import { ChevronDownIcon, ChevronUpIcon } from "@/components/ui/icons";
 
 interface SearchResponse {
   posts?: Post[];
 }
 
-const SEVERITY_LABELS: Record<number, string> = {
-  1: "Minimal",
-  2: "Low",
-  3: "Moderate",
-  4: "Severe",
-  5: "Critical",
-};
+const SEVERITY_LEVELS: SeverityLevel[] = [1, 2, 3, 4, 5];
 
 export function SearchResults({
   initialQuery,
@@ -28,8 +27,8 @@ export function SearchResults({
 }) {
   const [query, setQuery] = useState(initialQuery);
   const [agentFilter, setAgentFilter] = useState("");
-  const [minSeverity, setMinSeverity] = useState(1);
-  const [maxSeverity, setMaxSeverity] = useState(5);
+  const [minSeverity, setMinSeverity] = useState<SeverityLevel>(1);
+  const [maxSeverity, setMaxSeverity] = useState<SeverityLevel>(5);
   const [filtersOpen, setFiltersOpen] = useState(false);
 
   const [results, setResults] = useState<Post[]>(initialResults);
@@ -211,7 +210,7 @@ export function SearchResults({
                   aria-labelledby="filter-severity-label"
                   className="flex gap-1"
                 >
-                  {[1, 2, 3, 4, 5].map((lvl) => {
+                  {SEVERITY_LEVELS.map((lvl) => {
                     const inRange = lvl >= minSeverity && lvl <= maxSeverity;
                     return (
                       <button
@@ -231,9 +230,15 @@ export function SearchResults({
                             setMinSeverity(1);
                             setMaxSeverity(5);
                           } else if (lvl === minSeverity) {
-                            setMinSeverity(lvl + 1);
+                            const nextLevel = lvl + 1;
+                            if (isSeverityLevel(nextLevel)) {
+                              setMinSeverity(nextLevel);
+                            }
                           } else if (lvl === maxSeverity) {
-                            setMaxSeverity(lvl - 1);
+                            const previousLevel = lvl - 1;
+                            if (isSeverityLevel(previousLevel)) {
+                              setMaxSeverity(previousLevel);
+                            }
                           } else {
                             setMinSeverity(lvl);
                             setMaxSeverity(lvl);