task 00g/00k/00h/008: gofmt, remove ProviderWithFallback, stdlib helpers, shared prompt

- task 00g: fix gofmt violations (trailing whitespace, missing newlines,
  indentation) in 8 files; all pass gofmt -l now
- task 00k: remove unused ProviderWithFallback and its tests (YAGNI — no
  production caller existed; voice-level fallback via RunWithVoiceFallbacks
  already covers the real use case)
- task 00h: replace private splitLines/trimSpace/isSpace helpers in
  internal/batch/processor.go with strings.Split+ReplaceAll and
  strings.TrimSpace from the stdlib; remove the now-redundant tests
- task 008: extract buildEducationalPrompt into internal/image/prompt.go so
  the prompt-assembly policy (scene truncation cascade, char limit) lives in
  one place; both OpenAIClient and NanoBananaClient delegate to it

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2 files changed, 5 insertions, 178 deletions

diff --git a/internal/batch/processor.go b/internal/batch/processor.go
index 314d67f..2b002a9 100644
--- a/internal/batch/processor.go
+++ b/internal/batch/processor.go
@@ -31,10 +31,11 @@ func ReadBatchFile(filename string) ([]WordEntry, error) {
 	}
 
 	var entries []WordEntry
-	lines := string(content)
-
-	for _, line := range splitLines(lines) {
-		if line = trimSpace(line); line != "" {
+	// Normalize \r\n to \n before splitting so both Windows and Unix line
+	// endings are handled uniformly by strings.Split.
+	normalized := strings.ReplaceAll(string(content), "\r\n", "\n")
+	for _, line := range strings.Split(normalized, "\n") {
+		if line = strings.TrimSpace(line); line != "" {
 			entry := parseBatchLine(line)
 			if entry != nil {
 				entries = append(entries, *entry)
@@ -103,43 +104,3 @@ func parseBatchLine(line string) *WordEntry {
 	}
 }
 
-// splitLines splits a string by newlines, handling both \n and \r\n line endings.
-// Uses strings.Builder to avoid per-character heap allocations from += concatenation.
-func splitLines(s string) []string {
-	var lines []string
-	var current strings.Builder
-	for _, r := range s {
-		if r == '\n' {
-			lines = append(lines, current.String())
-			current.Reset()
-		} else if r != '\r' {
-			current.WriteRune(r)
-		}
-	}
-	if current.Len() > 0 {
-		lines = append(lines, current.String())
-	}
-	return lines
-}
-
-// trimSpace trims whitespace from string
-func trimSpace(s string) string {
-	start := 0
-	end := len(s)
-
-	// Trim from start
-	for start < end && isSpace(rune(s[start])) {
-		start++
-	}
-
-	// Trim from end
-	for end > start && isSpace(rune(s[end-1])) {
-		end--
-	}
-
-	return s[start:end]
-}
-
-func isSpace(r rune) bool {
-	return r == ' ' || r == '\t' || r == '\n' || r == '\r'
-}
diff --git a/internal/batch/processor_test.go b/internal/batch/processor_test.go
index fc4f7b0..8bc8079 100644
--- a/internal/batch/processor_test.go
+++ b/internal/batch/processor_test.go
@@ -163,137 +163,3 @@ func TestReadBatchFile_FileNotFound(t *testing.T) {
 	}
 }
 
-func TestSplitLines(t *testing.T) {
-	tests := []struct {
-		name  string
-		input string
-		want  []string
-	}{
-		{
-			name:  "unix line endings",
-			input: "line1\nline2\nline3",
-			want:  []string{"line1", "line2", "line3"},
-		},
-		{
-			name:  "windows line endings",
-			input: "line1\r\nline2\r\nline3",
-			want:  []string{"line1", "line2", "line3"},
-		},
-		{
-			name:  "mixed line endings",
-			input: "line1\nline2\r\nline3",
-			want:  []string{"line1", "line2", "line3"},
-		},
-		{
-			name:  "empty string",
-			input: "",
-			want:  nil,
-		},
-		{
-			name:  "single line no ending",
-			input: "single line",
-			want:  []string{"single line"},
-		},
-		{
-			name:  "trailing newline",
-			input: "line1\nline2\n",
-			want:  []string{"line1", "line2"},
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := splitLines(tt.input)
-			if !reflect.DeepEqual(got, tt.want) {
-				t.Errorf("splitLines() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
-
-func TestTrimSpace(t *testing.T) {
-	tests := []struct {
-		name  string
-		input string
-		want  string
-	}{
-		{
-			name:  "no whitespace",
-			input: "hello",
-			want:  "hello",
-		},
-		{
-			name:  "leading spaces",
-			input: "   hello",
-			want:  "hello",
-		},
-		{
-			name:  "trailing spaces",
-			input: "hello   ",
-			want:  "hello",
-		},
-		{
-			name:  "both sides",
-			input: "   hello   ",
-			want:  "hello",
-		},
-		{
-			name:  "tabs and spaces",
-			input: "\t  hello  \t",
-			want:  "hello",
-		},
-		{
-			name:  "newlines",
-			input: "\nhello\n",
-			want:  "hello",
-		},
-		{
-			name:  "all whitespace types",
-			input: " \t\n\rhello \t\n\r",
-			want:  "hello",
-		},
-		{
-			name:  "empty string",
-			input: "",
-			want:  "",
-		},
-		{
-			name:  "only whitespace",
-			input: "   \t\n\r   ",
-			want:  "",
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := trimSpace(tt.input)
-			if got != tt.want {
-				t.Errorf("trimSpace() = %q, want %q", got, tt.want)
-			}
-		})
-	}
-}
-
-func TestIsSpace(t *testing.T) {
-	tests := []struct {
-		r    rune
-		want bool
-	}{
-		{' ', true},
-		{'\t', true},
-		{'\n', true},
-		{'\r', true},
-		{'a', false},
-		{'1', false},
-		{'!', false},
-		{0, false},
-	}
-
-	for _, tt := range tests {
-		t.Run(string(tt.r), func(t *testing.T) {
-			if got := isSpace(tt.r); got != tt.want {
-				t.Errorf("isSpace(%q) = %v, want %v", tt.r, got, tt.want)
-			}
-		})
-	}
-}