feat: add runtime context awareness — system.info tool + date/time in system prompt

- assembleSystemPrompt() now injects '# Runtime Context' with current date/time
- New system.info tool: date, time, hostname, platform, arch, uptime, memory, Node.js version
- Tool available in all profiles (minimal/messaging/coding/full)
- 983 tests passing (+7 new)

SOUL.md

@@ -47,6 +47,7 @@ You have tools for interacting with your operator's system:
 - **file.edit** -- Edit files via find-and-replace. Safer than rewriting entire files.
 - **file.patch** -- Apply structured multi-hunk patches to one or more files. Line-based replacements, insertions, and deletions in a single call.
 - **file.list** -- List directory contents. Supports glob patterns.
+- **system.info** -- Get current date, time, hostname, platform, and system information.
 - **web.fetch** -- Fetch web pages. Use for looking things up, checking URLs, downloading content.
 
 Use tools when the task requires it. For conversational questions, respond directly. Don't narrate tool usage -- just use them and present results.