feat: full file context + patterns-repo support

Major improvements to review quality:

1. Full file context: fetch complete content of all modified files from
   the PR branch and include as reference. This eliminates false-positive
   "missing import" findings since the model sees the entire file.

2. Patterns repo: new --patterns-repo / PATTERNS_REPO flag fetches
   language idiom files from a separate Gitea repo (e.g. rodin/elixir-patterns)
   and includes them as review criteria.

3. Multi-file patterns: --patterns-files / PATTERNS_FILES accepts
   comma-separated file paths to fetch from the patterns repo.

New API methods:
- GetPullRequestFiles: list changed files in a PR
- GetFileContentRef: fetch file content from a specific branch/ref

Prompt changes:
- BuildSystemPrompt now accepts (conventions, patterns)
- BuildUserPrompt now accepts fileContext parameter
- File context displayed before diff for model reference
- Patterns presented as "review criteria" in system prompt

Composite action updated with patterns-repo and patterns-files inputs.

cmd/review-bot/main.go

@@ -1,6 +1,5 @@
 package main
 
-
 import (
 	"flag"
 	"fmt"
@@ -27,6 +26,8 @@ func main() {
 	llmAPIKey := flag.String("llm-api-key", envOrDefault("LLM_API_KEY", ""), "LLM API key")
 	llmModel := flag.String("llm-model", envOrDefault("LLM_MODEL", ""), "LLM model name")
 	conventionsFile := flag.String("conventions-file", envOrDefault("CONVENTIONS_FILE", ""), "Conventions file path in repo (e.g. CLAUDE.md)")
+	patternsRepo := flag.String("patterns-repo", envOrDefault("PATTERNS_REPO", ""), "Repo with language patterns (e.g. rodin/elixir-patterns)")
+	patternsFiles := flag.String("patterns-files", envOrDefault("PATTERNS_FILES", "README.md"), "Comma-separated file paths to fetch from patterns repo")
 	dryRun := flag.Bool("dry-run", false, "Print review to stdout instead of posting")
 	llmTemp := flag.Float64("llm-temperature", envOrDefaultFloat("LLM_TEMPERATURE", 0), "LLM temperature (0 = server default)")
 
@@ -79,7 +80,17 @@ func main() {
 	}
 	log.Printf("Diff size: %d bytes", len(diff))
 
-	// Step 3: Check CI status
+	// Step 3: Fetch full file content for modified files
+	fileContext := ""
+	files, err := giteaClient.GetPullRequestFiles(owner, repoName, prNumber)
+	if err != nil {
+		log.Printf("Warning: could not fetch PR files list: %v", err)
+	} else {
+		fileContext = fetchFileContext(giteaClient, owner, repoName, pr.Head.Ref, files)
+		log.Printf("Fetched full context for %d files", len(files))
+	}
+
+	// Step 4: Check CI status
 	ciPassed := true
 	ciDetails := ""
 	if pr.Head.Sha != "" {
@@ -92,7 +103,7 @@ func main() {
 		}
 	}
 
-	// Step 4: Load conventions file if specified
+	// Step 5: Load conventions file if specified
 	conventions := ""
 	if *conventionsFile != "" {
 		content, err := giteaClient.GetFileContent(owner, repoName, *conventionsFile)
@@ -104,11 +115,18 @@ func main() {
 		}
 	}
 
-	// Step 5: Build prompts
-	systemPrompt := review.BuildSystemPrompt(conventions)
-	userPrompt := review.BuildUserPrompt(pr.Title, pr.Body, diff, ciPassed, ciDetails)
+	// Step 6: Load patterns from external repo if specified
+	patterns := ""
+	if *patternsRepo != "" {
+		patterns = fetchPatterns(giteaClient, *patternsRepo, *patternsFiles)
+		log.Printf("Loaded patterns from %s (%d bytes)", *patternsRepo, len(patterns))
+	}
 
-	// Step 6: Call LLM
+	// Step 7: Build prompts
+	systemPrompt := review.BuildSystemPrompt(conventions, patterns)
+	userPrompt := review.BuildUserPrompt(pr.Title, pr.Body, diff, fileContext, ciPassed, ciDetails)
+
+	// Step 8: Call LLM
 	log.Printf("Sending to LLM (%s)...", *llmModel)
 	messages := []llm.Message{
 		{Role: "system", Content: systemPrompt},
@@ -121,14 +139,14 @@ func main() {
 	}
 	log.Printf("LLM response received (%d bytes)", len(response))
 
-	// Step 7: Parse response
+	// Step 9: Parse response
 	result, err := review.ParseResponse(response)
 	if err != nil {
 		log.Fatalf("Failed to parse LLM response: %v", err)
 	}
 	log.Printf("Verdict: %s (%d findings)", result.Verdict, len(result.Findings))
 
-	// Step 8: Format and post review
+	// Step 10: Format and post review
 	reviewBody := review.FormatMarkdown(result, *reviewerName)
 	event := review.GiteaEvent(result.Verdict)
 
@@ -146,6 +164,51 @@ func main() {
 	log.Printf("Review posted successfully!")
 }
 
+// fetchFileContext fetches the full content of modified files from the PR branch.
+func fetchFileContext(client *gitea.Client, owner, repo, ref string, files []gitea.ChangedFile) string {
+	var sb strings.Builder
+	for _, f := range files {
+		if f.Status == "removed" {
+			continue // Skip deleted files
+		}
+		content, err := client.GetFileContentRef(owner, repo, f.Filename, ref)
+		if err != nil {
+			log.Printf("Warning: could not fetch %s: %v", f.Filename, err)
+			continue
+		}
+		sb.WriteString(fmt.Sprintf("--- %s ---\n", f.Filename))
+		sb.WriteString("```\n")
+		sb.WriteString(content)
+		sb.WriteString("\n```\n\n")
+	}
+	return sb.String()
+}
+
+// fetchPatterns fetches pattern files from an external repo.
+func fetchPatterns(client *gitea.Client, patternsRepo, patternsFiles string) string {
+	parts := strings.SplitN(patternsRepo, "/", 2)
+	if len(parts) != 2 {
+		log.Printf("Warning: invalid patterns-repo format %q, expected owner/name", patternsRepo)
+		return ""
+	}
+	owner, repo := parts[0], parts[1]
+
+	var sb strings.Builder
+	for _, filepath := range strings.Split(patternsFiles, ",") {
+		filepath = strings.TrimSpace(filepath)
+		if filepath == "" {
+			continue
+		}
+		content, err := client.GetFileContent(owner, repo, filepath)
+		if err != nil {
+			log.Printf("Warning: could not fetch pattern file %s from %s: %v", filepath, patternsRepo, err)
+			continue
+		}
+		sb.WriteString(fmt.Sprintf("### %s/%s\n\n%s\n\n", patternsRepo, filepath, content))
+	}
+	return sb.String()
+}
+
 // evaluateCIStatus checks if all CI statuses indicate success.
 func evaluateCIStatus(statuses []gitea.CommitStatus) (passed bool, details string) {
 	if len(statuses) == 0 {