feat: complete MVP — all 14 tasks done

- Task 13: Full documentation (README, INSTALLATION, USAGE, ARCHITECTURE)
- Task 14: Release prep (CHANGELOG, RELEASE_CHECKLIST)
- Update PROJECT_STATE.md to reflect 100% completion

docs/USAGE.md

@@ -0,0 +1,151 @@
+# Usage Guide
+
+## Host Management
+
+### Add a Host
+
+Interactive mode:
+```bash
+hostkeeper add
+```
+
+With flags:
+```bash
+hostkeeper add myserver --host 192.168.1.10 --user admin --password mypass
+hostkeeper add myserver --host 10.0.0.1 --port 2222 --user root --key ~/.ssh/id_rsa
+hostkeeper add webserver --host example.com --user deploy --password secret --group production --tags web,frontend
+```
+
+Flags:
+- `--host` — hostname or IP address
+- `--port` — SSH port (default: 22)
+- `--user` — SSH username
+- `--password` — SSH password
+- `--key` — path to SSH private key
+- `--auth-type` — authentication type (password, key, both)
+- `--group` — host group for categorization
+- `--tags` — comma-separated tags
+- `--notes` — notes about the host
+
+### List Hosts
+
+```bash
+hostkeeper list
+hostkeeper ls  # alias
+```
+
+Filter by group or tag:
+```bash
+hostkeeper list --group production
+hostkeeper list --tag web
+```
+
+Output formats:
+```bash
+hostkeeper list --format table  # default
+hostkeeper list --format json
+```
+
+Sort options:
+```bash
+hostkeeper list --sort name      # default
+hostkeeper list --sort hostname
+hostkeeper list --sort group
+```
+
+### Connect to a Host
+
+Connect using system SSH (default, full interactive terminal):
+```bash
+hostkeeper connect myserver
+```
+
+Connect with Go SSH client (direct mode, no interactive shell):
+```bash
+hostkeeper connect myserver --direct
+```
+
+Custom timeout:
+```bash
+hostkeeper connect myserver --timeout 60
+```
+
+### Edit a Host
+
+Interactive mode:
+```bash
+hostkeeper edit myserver
+```
+
+With flags (only update what you specify):
+```bash
+hostkeeper edit myserver --host 10.0.0.1 --port 2222
+hostkeeper edit myserver --user root --name myserver-renamed
+hostkeeper edit myserver --group staging --tags backend
+```
+
+### Delete a Host
+
+With confirmation prompt:
+```bash
+hostkeeper delete myserver
+hostkeeper rm myserver  # alias
+```
+
+Skip confirmation:
+```bash
+hostkeeper delete myserver --force
+```
+
+## Data Management
+
+### Export
+
+Export all hosts, keys, and snippets to a JSON file:
+```bash
+hostkeeper export backup
+hostkeeper export backup.json
+```
+
+### Import
+
+Import from a previously exported JSON file:
+```bash
+hostkeeper import backup.json  # merge (default)
+hostkeeper import backup.json --strategy replace
+hostkeeper import backup.json --dry-run  # preview only
+```
+
+Merge strategies:
+- `merge` — keep existing data, add new items (default)
+- `replace` — replace all existing data with imported data
+
+## TUI Interface
+
+Launch the interactive terminal UI:
+```bash
+hostkeeper tui
+```
+
+Navigation:
+- `↑`/`k` — move up
+- `↓`/`j` — move down
+- `Enter` — select host
+- `q` — quit
+
+## Shell Completion
+
+Generate shell completion scripts:
+```bash
+hostkeeper completion bash > /etc/bash_completion.d/hostkeeper
+hostkeeper completion zsh > /usr/local/share/zsh/site-functions/_hostkeeper
+hostkeeper completion fish > ~/.config/fish/completions/hostkeeper.fish
+hostkeeper completion powershell > hostkeeper.ps1
+```
+
+## Global Flags
+
+- `--config` — path to custom config file
+- `-v`/`--verbose` — verbose output (-v for info, -vv for debug)
+- `--debug` — enable debug mode
+- `--help` — display help