Use gopsutil for cross-platform process detection

Replace pgrep with gopsutil/v4 for pure Go process detection.
Now fully cross-platform (Linux, FreeBSD, macOS, Windows) with
zero external exec calls. Add Taskfile and test fixture.

Taskfile.yml

@@ -0,0 +1,89 @@
+# https://taskfile.dev
+
+version: '3'
+
+vars:
+  BINARY: statusline
+  LDFLAGS: -s -w
+
+tasks:
+  default:
+    desc: Build the statusline binary
+    cmds:
+      - task: build
+
+  build:
+    desc: Build with stripped symbols
+    cmds:
+      - go build -ldflags="{{.LDFLAGS}}" -o {{.BINARY}} .
+    sources:
+      - "*.go"
+      - go.mod
+      - go.sum
+    generates:
+      - "{{.BINARY}}"
+
+  build:debug:
+    desc: Build with debug symbols
+    cmds:
+      - go build -o {{.BINARY}} .
+
+  run:
+    desc: Run with test fixture
+    deps: [build]
+    cmds:
+      - cat test/fixture.json | ./{{.BINARY}}
+
+  test:
+    desc: Run with test fixture and show output
+    deps: [build]
+    cmds:
+      - echo "=== Output ==="
+      - cat test/fixture.json | ./{{.BINARY}}
+      - echo ""
+      - echo "=== Timing (single run) ==="
+      - time sh -c 'cat test/fixture.json | ./{{.BINARY}} > /dev/null'
+
+  bench:
+    desc: Benchmark Go vs Shell (100 runs)
+    deps: [build]
+    cmds:
+      - |
+        echo "=== Pure Go (100 runs) ==="
+        time for i in $(seq 1 100); do cat test/fixture.json | ./{{.BINARY}} >/dev/null; done
+        echo ""
+        echo "=== Shell (100 runs) ==="
+        time for i in $(seq 1 100); do cat test/fixture.json | ./statusline.sh >/dev/null; done
+    silent: false
+
+  bench:go:
+    desc: Benchmark Go only (100 runs)
+    deps: [build]
+    cmds:
+      - |
+        echo "=== Pure Go (100 runs) ==="
+        time for i in $(seq 1 100); do cat test/fixture.json | ./{{.BINARY}} >/dev/null; done
+
+  tidy:
+    desc: Run go mod tidy
+    cmds:
+      - go mod tidy
+
+  clean:
+    desc: Remove built binary
+    cmds:
+      - rm -f {{.BINARY}}
+
+  size:
+    desc: Show binary size
+    deps: [build]
+    cmds:
+      - ls -lh {{.BINARY}}
+
+  install:
+    desc: Install to ~/.claude/
+    deps: [build]
+    cmds:
+      - mkdir -p ~/.claude
+      - cp {{.BINARY}} ~/.claude/{{.BINARY}}
+      - echo "Installed to ~/.claude/{{.BINARY}}"