Remove vestigial --resolve-collisions flag

Hash-based IDs make collision resolution unnecessary. The flag was
already non-functional (handleCollisions returns error on collision
regardless of flag value).

Removed:
- --resolve-collisions flag from bd import
- ResolveCollisions field from ImportOptions and importer.Options
- All references in daemon, auto-import, and tests
- Updated error messages to reflect hash IDs don't collide

All import tests pass.

Amp-Thread-ID: https://ampcode.com/threads/T-47dfa0cc-bb71-4467-ac86-f0966a7c5d58
Co-authored-by: Amp <amp@ampcode.com>

internal/importer/importer.go

@@ -15,7 +15,6 @@ import (
 
 // Options contains import configuration
 type Options struct {
-	ResolveCollisions    bool // Auto-resolve collisions by remapping to new IDs
 	DryRun               bool // Preview changes without applying them
 	SkipUpdate           bool // Skip updating existing issues (create-only mode)
 	Strict               bool // Fail on any error (dependencies, labels, etc.)

internal/rpc/server_export_import_auto.go

@@ -209,8 +209,7 @@ func (s *Server) checkAndAutoImportIfStale(req *Request) error {
 	importFunc := func(ctx context.Context, issues []*types.Issue) (created, updated int, idMapping map[string]string, err error) {
 		// Use the importer package to perform the actual import
 		result, err := importer.ImportIssues(ctx, dbPath, store, issues, importer.Options{
-			ResolveCollisions: false, // Do NOT resolve collisions - update existing issues by ID
-			RenameOnImport:    true,  // Auto-rename prefix mismatches
+			RenameOnImport: true, // Auto-rename prefix mismatches
 			// Note: SkipPrefixValidation is false by default, so we validate and rename
 		})
 		if err != nil {