feat(#137): add doc-map input for path-scoped doc injection

- New --doc-map flag (DOC_MAP_FILE env var): path to YAML config mapping
  source path globs to governing design docs
- New --doc-map-max-bytes flag (DOC_MAP_MAX_BYTES env var): cap on total
  injected doc content, default 100KB
- review/docmap.go: DocMapConfig parsing, glob matching with ** support,
  doc loading via VCS with directory expansion and size guard
- budget.Sections: new DesignDocs field, trimmed after conventions
- budget.buildResult: injects DesignDocs under ## Design Documents heading
- action.yml: doc-map and doc-map-max-bytes inputs wired to env vars
- CHANGELOG.md: created with unreleased entry
- Tests: ParseDocMapConfig, MatchDocs, globMatch, LoadMatchingDocs

cmd/review-bot/main.go

@@ -97,6 +97,8 @@ func main() {
 	aicoreAuthURL := flag.String("aicore-auth-url", envOrDefault("AICORE_AUTH_URL", ""), "SAP AI Core auth URL (for provider=aicore)")
 	aicoreAPIURL := flag.String("aicore-api-url", envOrDefault("AICORE_API_URL", ""), "SAP AI Core API URL (for provider=aicore)")
 	aicoreResourceGroup := flag.String("aicore-resource-group", envOrDefault("AICORE_RESOURCE_GROUP", "default"), "SAP AI Core resource group (for provider=aicore)")
+	docMapFile := flag.String("doc-map", envOrDefault("DOC_MAP_FILE", ""), "Path to YAML file mapping source path globs to governing design docs")
+	docMapMaxBytes := flag.Int("doc-map-max-bytes", envOrDefaultInt("DOC_MAP_MAX_BYTES", review.DefaultDocMapMaxBytes), "Maximum bytes of injected doc content (default 102400)")
 
 	flag.Parse()
 
@@ -350,6 +352,46 @@ func main() {
 		slog.Debug("loaded system prompt file", "file", *systemPromptFile, "bytes", len(additionalPrompt))
 	}
 
+	// Step 6c: Load path-scoped design docs if doc-map specified
+	designDocs := ""
+	if *docMapFile != "" {
+		resolvedDocMap, err := validateWorkspacePath(*docMapFile, "doc-map")
+		if err != nil {
+			slog.Error("invalid doc-map path", "error", err)
+			os.Exit(1)
+		}
+		docMapCfg, err := review.ParseDocMapConfig(resolvedDocMap)
+		if err != nil {
+			slog.Error("failed to parse doc-map file", "file", *docMapFile, "error", err)
+			os.Exit(1)
+		}
+
+		// Collect changed file paths from the PR for intersection.
+		var changedPaths []string
+		for _, f := range files {
+			changedPaths = append(changedPaths, f.Filename)
+		}
+
+		matchedDocs := review.MatchDocs(docMapCfg, changedPaths)
+		slog.Debug("doc-map: matched docs", "count", len(matchedDocs), "docs", matchedDocs)
+
+		if len(matchedDocs) > 0 {
+			docMapOpts := review.DocMapOptions{MaxBytes: *docMapMaxBytes}
+			designDocs, err = review.LoadMatchingDocs(ctx, vcs, owner, repoName, matchedDocs, docMapOpts)
+			if err != nil {
+				// Non-fatal: individual missing files are already warned; log and continue.
+				slog.Warn("doc-map: partial failure loading docs", "error", err)
+			}
+			if designDocs != "" {
+				slog.Info("doc-map: injected design docs", "matched", len(matchedDocs), "bytes", len(designDocs))
+			} else {
+				slog.Debug("doc-map: no doc content loaded (all files missing or empty)")
+			}
+		} else {
+			slog.Debug("doc-map: no changed paths matched any mapping")
+		}
+	}
+
 	// Step 7: Budget-aware prompt assembly
 	var systemBase string
 	if persona != nil {
@@ -365,6 +407,7 @@ func main() {
 		SystemBase:  systemBase,
 		Patterns:    patterns,
 		Conventions: conventions,
+		DesignDocs:  designDocs,
 		FileContext: fileContext,
 		Diff:        diff,
 		UserMeta:    review.BuildUserMeta(pr.Title, pr.Body, ciPassed, ciDetails),