Add terminal package with secure ReadPassword helper

Provides echo-suppressed password prompting via golang.org/x/term for
CLI login commands. Added as a platform standard in engineering-standards.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -37,6 +37,7 @@ go test ./auth/ -run TestCacheExpiry
 | `web` | Session cookies, auth middleware, template rendering for htmx UIs |
 | `health` | REST and gRPC health check handlers |
 | `archive` | tar.zst snapshots with SQLite-aware backup (VACUUM INTO) |
+| `terminal` | Secure terminal input (echo-suppressed password prompts) |
 
 ## Import Pattern
 
@@ -63,6 +64,7 @@ db --> (modernc.org/sqlite)
 grpcserver --> auth, config
 health --> db
 httpserver --> config
+terminal --> (golang.org/x/term)
 web --> auth, csrf
 ```