feat: track spawned processes (execve count) per variation

Add a new 'Spawned Processes' data point that counts the number of
processes each package manager spawns (via execve syscalls) during
install. This is captured per-variation since different states (clean,
cache, lockfile, etc.) may produce different process counts.

## How it works

After each benchmark completes, a separate strace run is performed for
each package manager under the same variation state:

1. `process-count.sh` — wraps a single install with
   `strace -f -e trace=execve` and counts execve() calls
2. `collect-process-count.js` — aggregates per-PM counts into
   `process-count.json` (same format as package-count.json)
3. `collect_process_count` in common.sh — orchestrates the strace
   runs for all included PMs using BENCH_PREPARE_BASE + setup commands

The strace run is separate from the timed benchmark to avoid overhead.

## Backend changes

- `scripts/process-count.sh` — new: strace wrapper per PM
- `scripts/collect-process-count.js` — new: aggregation script
- `scripts/variations/common.sh` — extracted bare BENCH_INSTALL_*
  commands (no log redirects) for reuse; added collect_process_count()
- All 8 standard variation scripts — call collect_process_count
- `scripts/process-results.sh` — copy process-count.json to results
- `scripts/setup.sh` — ensure strace is installed

## Frontend changes

- `ProcessCountData` / `ProcessCountTableRow` types
- `use-process-count-data.ts` hook (mirrors use-package-count-data)
- `ProcessCountTable` component with Terminal icon, sortable columns,
  locale-formatted numbers
- Integrated into variation page below Package Count Data
- `getAvailablePackageManagersFromProcessCount` utility

Author: baudbot-agent

app/src/components/variation/index.tsx

@@ -5,7 +5,9 @@ import { ERROR_MESSAGES } from "@/constants";
 import { VariationChart } from "@/components/variation/chart";
 import { VariationTable } from "@/components/variation/table";
 import { PackageCountTable } from "@/components/variation/package-count-table";
+import { ProcessCountTable } from "@/components/variation/process-count-table";
 import { usePackageCountData } from "@/hooks/use-package-count-data";
+import { useProcessCountData } from "@/hooks/use-process-count-data";
 import { useFixtureFilter } from "@/contexts/fixture-filter-context";
 import {
   sortFixtures,
@@ -14,6 +16,7 @@ import {
   getFixtureId,
   getAvailablePackageManagers,
   getAvailablePackageManagersFromPackageCount,
+  getAvailablePackageManagersFromProcessCount,
   isTaskExecutionVariation,
   isRegistryVariation,
 } from "@/lib/utils";
@@ -46,6 +49,11 @@ export const VariationPage = () => {
     loading: packageCountLoading,
     error: packageCountError,
   } = usePackageCountData(variation as Variation);
+  const {
+    processCountData,
+    loading: processCountLoading,
+    error: processCountError,
+  } = useProcessCountData(variation as Variation);
   const { enabledFixtures } = useFixtureFilter();
 
   // Handle deep linking to sections and fixtures
@@ -111,6 +119,9 @@ export const VariationPage = () => {
   const filteredPackageCountData = packageCountData.filter((item) =>
     enabledFixtures.has(item.fixture),
   );
+  const filteredProcessCountData = processCountData.filter((item) =>
+    enabledFixtures.has(item.fixture),
+  );
 
   // Filter package managers to only show those with data for this variation
   const packageManagers = getAvailablePackageManagers(
@@ -125,6 +136,13 @@ export const VariationPage = () => {
       allPackageManagers,
     );
 
+  // Filter package managers for process count data to only show those with actual data
+  const processCountPackageManagers =
+    getAvailablePackageManagersFromProcessCount(
+      filteredProcessCountData,
+      allPackageManagers,
+    );
+
   // Check if this is a task execution variation or registry variation
   const isTaskExecution = isTaskExecutionVariation(variation as string);
   const isRegistry = isRegistryVariation(variation as string);
@@ -137,6 +155,7 @@ export const VariationPage = () => {
         perPackageChart: "Task Execution Time by Fixture",
         perPackageTable: "Task Execution Time Data",
         packageCountTable: "Package Count Data",
+        processCountTable: "Spawned Processes Data",
       }
     : isRegistry
       ? {
@@ -145,13 +164,15 @@ export const VariationPage = () => {
           perPackageChart: "Registry Install Time by Fixture",
           perPackageTable: "Registry Install Time Data",
           packageCountTable: "Package Count Data",
+          processCountTable: "Spawned Processes Data",
         }
       : {
           totalChart: "Total Install Time by Fixture",
           totalTable: "Total Install Time Data",
           perPackageChart: "Per Package Install Time by Fixture",
           perPackageTable: "Per Package Install Time Data",
           packageCountTable: "Package Count Data",
+          processCountTable: "Spawned Processes Data",
         };
 
   // Section IDs for deep linking
@@ -161,6 +182,7 @@ export const VariationPage = () => {
     totalTable: createSectionId(titles.totalTable),
     perPackageTable: createSectionId(titles.perPackageTable),
     packageCountTable: createSectionId(titles.packageCountTable),
+    processCountTable: createSectionId(titles.processCountTable),
   };
 
   return (
@@ -240,6 +262,28 @@ export const VariationPage = () => {
             />
           </div>
         ) : null}
+
+        {/* 6. Spawned processes data table */}
+        {processCountLoading ? (
+          <div className="text-center text-muted-foreground">
+            Loading process count data...
+          </div>
+        ) : processCountError ? (
+          <div className="text-center text-destructive">
+            Error loading process count data: {processCountError}
+          </div>
+        ) : filteredProcessCountData.length > 0 ? (
+          <div id={sectionIds.processCountTable}>
+            <ProcessCountTable
+              title="Spawned Processes Data"
+              description="Number of processes spawned (execve calls) by each package manager during install"
+              processCountData={filteredProcessCountData}
+              packageManagers={processCountPackageManagers}
+              versions={chartData.versions}
+              currentVariation={variation as string}
+            />
+          </div>
+        ) : null}
       </div>
 
       <div className="space-y-8">