Adopt repo standards: scaffold, policies, lint-clean (closes #1)

Add the standard scaffold and bring the tree to a clean lint under the
vendored `default: all` config. New: `script/` Scripts-to-Rule-Them-All
entrypoints with the `Makefile` reduced to thin shims; a `Dockerfile`
whose `lint` and `test` phases gate the build (final stage depends on
both); a `.gitea/workflows/` CI running `script/cibuild`; the vendored
`.golangci.yml`; `REPO_POLICIES.md`; `.editorconfig`; `.dockerignore`; a
`LICENSE` (WTFPL) and `TODO.md`; and a comprehensive `.gitignore`.

The 211 lint findings were fixed, not suppressed: package-level state
became functions/fields/a command constructor, magic numbers became named
constants, `ctx` is threaded into the probes, the loop functions were
split to cut complexity, and the deprecated `+build` tags were dropped.
Behavior is unchanged. The only annotations are justified `//nolint:gosec`
on the `ping`/`curl` subprocess calls (G204, fixed argv) and the
operator-chosen log file (G304), matching the reference repos.

`make check` is green (lint and tests run in Docker).

Model: opus-4-8

internal/monitor/styles_test.go

@@ -1,104 +1,48 @@
 //go:build linux
-// +build linux
 
-package monitor
+package monitor_test
 
 import (
 	"testing"
 
 	tcell "github.com/gdamore/tcell/v2"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/monitor"
 )
 
-// TestMeterColorForValue tests the MeterColorForValue function
 func TestMeterColorForValue(t *testing.T) {
-	tests := []struct {
-		name      string
-		value     int
-		maxValue  int
-		reverse   bool
-		wantColor tcell.Style
-	}{
-		// Reverse mode tests (low is good, high is bad)
-		{
-			name:      "reverse mode: 0% (best)",
-			value:     0,
-			maxValue:  10,
-			reverse:   true,
-			wantColor: CBrightGreen,
-		},
-		{
-			name:      "reverse mode: 10% (good)",
-			value:     1,
-			maxValue:  10,
-			reverse:   true,
-			wantColor: CBrightGreen,
-		},
-		{
-			name:      "reverse mode: 50% (medium)",
-			value:     5,
-			maxValue:  10,
-			reverse:   true,
-			wantColor: CYellow,
-		},
-		{
-			name:      "reverse mode: 90% (bad)",
-			value:     9,
-			maxValue:  10,
-			reverse:   true,
-			wantColor: CRed,
-		},
-		{
-			name:      "reverse mode: 100% (worst)",
-			value:     10,
-			maxValue:  10,
-			reverse:   true,
-			wantColor: CRed,
-		},
+	t.Parallel()
 
-		// Normal mode tests (high is good, low is bad)
-		{
-			name:      "normal mode: 0% (worst)",
-			value:     0,
-			maxValue:  10,
-			reverse:   false,
-			wantColor: CRed,
-		},
-		{
-			name:      "normal mode: 10% (bad)",
-			value:     1,
-			maxValue:  10,
-			reverse:   false,
-			wantColor: CRed,
-		},
-		{
-			name:      "normal mode: 50% (medium)",
-			value:     5,
-			maxValue:  10,
-			reverse:   false,
-			wantColor: CYellow,
-		},
-		{
-			name:      "normal mode: 90% (good)",
-			value:     9,
-			maxValue:  10,
-			reverse:   false,
-			wantColor: CBrightGreen,
-		},
-		{
-			name:      "normal mode: 100% (best)",
-			value:     10,
-			maxValue:  10,
-			reverse:   false,
-			wantColor: CBrightGreen,
-		},
+	green := tcell.StyleDefault.Foreground(tcell.ColorGreen).Bold(true)
+	yellow := tcell.StyleDefault.Foreground(tcell.ColorYellow)
+	red := tcell.StyleDefault.Foreground(tcell.ColorRed)
+
+	tests := []struct {
+		name            string
+		value, maxValue int
+		reverse         bool
+		want            tcell.Style
+	}{
+		{"reverse 0% best", 0, 10, true, green},
+		{"reverse 10% good", 1, 10, true, green},
+		{"reverse 50% medium", 5, 10, true, yellow},
+		{"reverse 90% bad", 9, 10, true, red},
+		{"reverse 100% worst", 10, 10, true, red},
+		{"normal 0% worst", 0, 10, false, red},
+		{"normal 10% bad", 1, 10, false, red},
+		{"normal 50% medium", 5, 10, false, yellow},
+		{"normal 90% good", 9, 10, false, green},
+		{"normal 100% best", 10, 10, false, green},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got := MeterColorForValue(tt.value, tt.maxValue, tt.reverse)
-			if got != tt.wantColor {
+			t.Parallel()
+
+			got := monitor.MeterColorForValue(tt.value, tt.maxValue, tt.reverse)
+			if got != tt.want {
 				t.Errorf("MeterColorForValue(%d, %d, %v) = %v, want %v",
-					tt.value, tt.maxValue, tt.reverse, got, tt.wantColor)
+					tt.value, tt.maxValue, tt.reverse, got, tt.want)
 			}
 		})
 	}