feat: tapes config command

[jpmcb]

• ✨ New config command for get, list, and set configs: these are persisted to the given / found .tapes/ directory (see the dotdir package)
• ✨ New pkg/config package that handles all default configs, client configs, proxy configs, etc. This also handles loading / saving configurations
• ✨ tapes init now supports some sane presets as well as a --preset URL flag: tapes init --preset https://example.com/raw/config.toml
• 🧹 The dotdir.Manager Target function now falls through to returning "", nil (i.e., the empty state) to denote that no target directory was found to use.
• 🧹 Aligned the various flags around *-target especially as these have drifted in the client commands like search and chat
• 🧹 The cli/*/main.go files now handle errors raised by cmd.Execute (possibly raised during now using preRunE throughout command bootstrapping)