Dev (#25)

Delete .Jules directory

fix(command): use markdown formatting for slash command output

Rewrite all command outputs to use proper markdown (bold headers, bullet
lists, code backticks) so glamour and Telegram renderers display them
correctly. Also auto-generate release notes summary instead of static
placeholder.

feat(command): add slash command framework with 7 built-in commands

Introduce internal/command/ package with a registry-based slash command
framework. Commands are intercepted in processMessage() before the LLM
call, working across all channels (TUI, Telegram, Discord, etc.).

Built-in commands: /help, /new, /version, /status, /cron, /skills, /memory

fix(version): fallback to module version for go install builds

Use runtime/debug.ReadBuildInfo() so that binaries installed via
go install display the tagged module version instead of "dev".

feat(cli): add golem version command

Prints version, OS, and architecture (e.g. "golem v0.5.3 linux/amd64").
Version is injected at build time via -ldflags.

fix: resolve empty reply and heartbeat leak to channels

- Agent loop now captures LLM content on every iteration, not only when
  tool calls are absent, preventing the "Processing complete." fallback
  from masking actual responses.
- Channel manager filters outbound messages with metadata type
  "heartbeat" so internal health-check logs no longer reach end users.