Support closing keywords with URL references (#36221)

## Summary

This PR adds support for closing keywords (`closes`, `fixes`, `reopens`,
etc.) with full URL references in markdown links.

**Before:**
- `closes #123` ✅ works
- `closes org/repo#123` ✅ works  
- `Closes [this issue](https://gitea.io/user/repo/issues/123)` ❌ didn't
work
- `Fixes [#456](https://gitea.io/org/project/issues/456)` ❌ didn't work

**After:**
All of the above now work correctly.

## Problem

When users reference issues using full URLs in markdown links (e.g.,
`Closes [this issue](https://gitea.io/user/repo/issues/123)`), the
closing keywords were not detected. This was because the URL processing
code explicitly stated:

```go
// Note: closing/reopening keywords not supported with URLs
```

Both methods of writing the reference render the same in the UI, so
users expected the closing keywords to behave the same.

## Solution

The fix works by:
1. Passing the original (unstripped) content to
`findAllIssueReferencesBytes`
2. When processing URL links from markdown, finding the URL position in
the original content
3. For markdown links `[text](url)`, finding the opening bracket `[`
position
4. Using that position to detect closing keywords before the link

## Testing

Added test cases for:
- `Closes [this issue](url)` - single URL with closing keyword
- `This fixes [#456](url)` - keyword in middle of text
- `Reopens [PR](url)` - reopen keyword with pull request URL
- Multiple URLs where only one has a closing keyword

All existing tests continue to pass.

Fixes #27549

modules/references/references.go

@@ -248,7 +248,7 @@ func FindAllIssueReferencesMarkdown(content string) []IssueReference {
 
 func findAllIssueReferencesMarkdown(content string) []*rawReference {
 	bcontent, links := mdstripper.StripMarkdownBytes([]byte(content))
-	return findAllIssueReferencesBytes(bcontent, links)
+	return findAllIssueReferencesBytes(bcontent, links, []byte(content))
 }
 
 func convertFullHTMLReferencesToShortRefs(re *regexp.Regexp, contentBytes *[]byte) {
@@ -326,7 +326,7 @@ func FindAllIssueReferences(content string) []IssueReference {
 	} else {
 		log.Debug("No GiteaIssuePullPattern pattern")
 	}
-	return rawToIssueReferenceList(findAllIssueReferencesBytes(contentBytes, []string{}))
+	return rawToIssueReferenceList(findAllIssueReferencesBytes(contentBytes, []string{}, nil))
 }
 
 // FindRenderizableReferenceNumeric returns the first unvalidated reference found in a string.
@@ -406,7 +406,8 @@ func FindRenderizableReferenceAlphanumeric(content string) *RenderizableReferenc
 }
 
 // FindAllIssueReferencesBytes returns a list of unvalidated references found in a byte slice.
-func findAllIssueReferencesBytes(content []byte, links []string) []*rawReference {
+// originalContent is optional and used to detect closing/reopening keywords for URL references.
+func findAllIssueReferencesBytes(content []byte, links []string, originalContent []byte) []*rawReference {
 	ret := make([]*rawReference, 0, 10)
 	pos := 0
 
@@ -470,10 +471,27 @@ func findAllIssueReferencesBytes(content []byte, links []string) []*rawReference
 			default:
 				continue
 			}
-			// Note: closing/reopening keywords not supported with URLs
-			bytes := []byte(parts[1] + "/" + parts[2] + sep + parts[4])
-			if ref := getCrossReference(bytes, 0, len(bytes), true, false); ref != nil {
+			refBytes := []byte(parts[1] + "/" + parts[2] + sep + parts[4])
+			if ref := getCrossReference(refBytes, 0, len(refBytes), true, false); ref != nil {
 				ref.refLocation = nil
+				// Detect closing/reopening keywords by finding the URL position in original content
+				if originalContent != nil {
+					if idx := bytes.Index(originalContent, []byte(link)); idx > 0 {
+						// For markdown links [text](url), find the opening bracket before the URL
+						// to properly detect keywords like "closes [text](url)"
+						searchStart := idx
+						if idx >= 2 && originalContent[idx-1] == '(' {
+							// Find the matching '[' for this markdown link
+							bracketIdx := bytes.LastIndex(originalContent[:idx-1], []byte{'['})
+							if bracketIdx >= 0 {
+								searchStart = bracketIdx
+							}
+						}
+						action, location := findActionKeywords(originalContent, searchStart)
+						ref.action = action
+						ref.actionLocation = location
+					}
+				}
 				ret = append(ret, ref)
 			}
 		}