fix: honor parser params and image VLM system_prompt in Go ingestion (#17334)

## Summary
Fix the Go ingestion pipeline so that several parser setup switches and
the
image VLM prompt are actually honored end-to-end (previously the DSL
fields
existed but the Go code never read them).

- **DOCX** (`docx_parser.go`, `docx_postprocess.go`): read `remove_toc`
and
  `remove_header_footer`; apply to both JSON and markdown output paths
  (outline-based TOC removal with a text-heuristic fallback, plus
  header/footer section filtering).
- **HTML** (`html_parser.go`, `html_postprocess.go`, `text_toc.go`):
read
`remove_header_footer` (pre-parse strip of `<header>`/`<footer>` and
ARIA
`banner`/`contentinfo`) and `remove_toc` (post-parse
`remove_contents_table`
  heuristic).
- **Markdown** (`markdown_parser.go`): read `flatten_media_to_text` and
force
  media blocks to text when enabled.
- **Image VLM** (`media_dispatch.go`): read `system_prompt` instead of
`prompt`
  so the user-configured image VLM prompt is no longer silently dropped
  (`prompt` remains the video family key).

All flags are wired through `ConfigureFromSetup`, which the dispatch
layer
already invokes for every family, so the behavior is live rather than
dead code.

## Test plan
- New unit tests: `docx_postprocess_test.go`, `html_parser_test.go`,
`text_toc_test.go`, `markdown_parser_test.go`, `media_dispatch_test.go`.
- `bash build.sh --test ./internal/parser/parser/...
./internal/ingestion/component/...`

## Notes
- The `File` component is excluded from this migration scope.
- Relates to the Python→Go parity diff (Parser 1.8–1.11, 1.15).

internal/parser/parser/text_toc_test.go

@@ -0,0 +1,108 @@
+package parser
+
+import (
+	"reflect"
+	"testing"
+)
+
+// TestRemoveContentsTable mirrors the Python remove_contents_table
+// (rag/nlp/__init__.py:937-965). It locates a TOC heading
+// (contents/目录/目次/...), drops it, then drops the following
+// entries that share a common prefix with the first TOC entry.
+func TestRemoveContentsTable(t *testing.T) {
+	cases := []struct {
+		name  string
+		items []map[string]any
+		eng   bool
+		want  []map[string]any
+	}{
+		{
+			name:  "no TOC heading → unchanged",
+			items: []map[string]any{{"text": "Intro"}, {"text": "Body"}},
+			eng:   false,
+			want:  []map[string]any{{"text": "Intro"}, {"text": "Body"}},
+		},
+		{
+			name: "Chinese 目录 heading + first TOC entry removed",
+			items: []map[string]any{
+				{"text": "前言"},
+				{"text": "目录"},
+				{"text": "第一章 概述"},
+				{"text": "第二章 方法"},
+				{"text": "正文开始"},
+			},
+			eng: false,
+			// Python remove_contents_table drops the heading and the
+			// first entry after it (prefix "第一章"). Subsequent
+			// entries with a different prefix ("第二章") are kept
+			// because re.match("第一章", "第二章 方法") fails.
+			want: []map[string]any{
+				{"text": "前言"},
+				{"text": "第二章 方法"},
+				{"text": "正文开始"},
+			},
+		},
+		{
+			name: "English Contents heading + first TOC entry removed",
+			items: []map[string]any{
+				{"text": "Intro"},
+				{"text": "Contents"},
+				{"text": "Chapter 1 Overview"},
+				{"text": "Chapter 2 Method"},
+				{"text": "Body starts"},
+			},
+			eng: true,
+			want: []map[string]any{
+				{"text": "Intro"},
+				{"text": "Chapter 2 Method"},
+				{"text": "Body starts"},
+			},
+		},
+		{
+			name: "目录 heading with no following entry → heading dropped only",
+			items: []map[string]any{
+				{"text": "前言"},
+				{"text": "目录"},
+			},
+			eng: false,
+			want: []map[string]any{
+				{"text": "前言"},
+			},
+		},
+		{
+			name: "prefix-matching subsequent entries collapse non-matching gap",
+			items: []map[string]any{
+				{"text": "前言"},
+				{"text": "目录"},
+				{"text": "第一节 概述"},
+				{"text": "杂项"},
+				{"text": "第一节 背景"},
+				{"text": "正文"},
+			},
+			eng: false,
+			// prefix="第一节"; after dropping heading + first entry,
+			// scan finds "第一节 背景" at j=2 (gap "杂项" at j=1);
+			// Python deletes [i, j) = the gap, keeps the match.
+			want: []map[string]any{
+				{"text": "前言"},
+				{"text": "第一节 背景"},
+				{"text": "正文"},
+			},
+		},
+		{
+			name:  "empty input → unchanged",
+			items: nil,
+			eng:   false,
+			want:  nil,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := removeContentsTable(tc.items, tc.eng)
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("got %v, want %v", got, tc.want)
+			}
+		})
+	}
+}