fix(indexer): index full file paths and real offsets in bleve (#39405)

The bleve path token filter added in
https://github.com/go-gitea/gitea/pull/32210 never generated the full
path of a file, so searching a file by its path (e.g. `potato/ham`)
found nothing. It also gave the path tokens made-up offsets instead of
their position in the path.

The filter is replaced by a tokenizer that emits the raw path suffixes
starting at each segment and word (`potato/ham.md`, `ham.md`). Paths
below the root now match too, as do names containing `-` or spaces and
dotfiles. An exact file name also ranks above files inside a directory
with the same name.

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/indexer/code/bleve/token_path.go

@@ -0,0 +1,38 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package bleve
+
+import (
+	"github.com/blevesearch/bleve/v2/analysis"
+	unicode_tokenizer "github.com/blevesearch/bleve/v2/analysis/tokenizer/unicode"
+	"github.com/blevesearch/bleve/v2/registry"
+)
+
+const pathTokenizerName = "pathTokenizer"
+
+// pathTokenizer emits the path suffixes starting at each segment and word, for the prefix query in Search
+type pathTokenizer struct{}
+
+func (pathTokenizer) Tokenize(input []byte) (ret analysis.TokenStream) {
+	words := unicode_tokenizer.NewUnicodeTokenizer().Tokenize(input)
+	for start := range input {
+		isWordStart := len(words) > 0 && words[0].Start == start
+		if isWordStart {
+			words = words[1:]
+		}
+		if start == 0 || input[start-1] == '/' || isWordStart {
+			ret = append(ret, &analysis.Token{
+				Start:    start,
+				End:      len(input),
+				Term:     input[start:],
+				Position: len(ret) + 1,
+			})
+		}
+	}
+	return ret
+}
+
+func pathTokenizerConstructor(_ map[string]any, _ *registry.Cache) (analysis.Tokenizer, error) {
+	return pathTokenizer{}, nil
+}