feat(cli,config): add config file, providers/models listing, and help command

README.md

@@ -36,7 +36,7 @@ After installation, `opencode-usage` is available globally.
 
 ## Usage
 
-The CLI has two subcommands: `run` (default) and `insights`.
+The CLI has these subcommands: `run` (default), `insights`, `providers`, `models`, and `help`.
 
 ### `run` — Token usage statistics
 
@@ -63,6 +63,27 @@ opencode-usage run --by model --json | jq '.rows[].label'
 opencode-usage run --since 7d --compare
 ```
 
+### `providers` / `models` — list available IDs
+
+Both list what opencode itself exposes (`opencode models`), so they stay in
+sync with your setup. Providers marked with `*` have credentials in
+opencode's `auth.json`.
+
+```bash
+opencode-usage providers
+opencode-usage models
+opencode-usage models --provider opencode-go --id
+opencode-usage providers --json
+```
+
+### `help` — command help
+
+```bash
+opencode-usage help            # general help, config docs, examples
+opencode-usage help run
+opencode-usage help insights
+```
+
 ### `insights` — LLM-powered analysis
 
 Analyze your OpenCode sessions and generate an HTML report with workflow insights, friction patterns, agent performance, and actionable suggestions.
@@ -108,6 +129,23 @@ Requires an API key for the LLM provider — set via environment variable (e.g.
 
 ## Configuration
 
+### Config file
+
+Optional `~/.config/opencode-usage/config.toml` sets defaults. CLI flags
+always win over config values, which win over built-in defaults.
+
+```toml
+[defaults]
+days = 7          # or weeks / months
+by = "day"        # minute, hour, day, week, month, model, agent, provider, session
+sort = "tokens"   # tokens, cost, calls
+
+[insights]
+preferred_models = ["opencode-go/kimi-k3"]  # shown first in the model picker
+```
+
+### Environment variables
+
 | Environment Variable | Description |
 |---|---|
 | `OPENCODE_DB` | Override database path (default: auto-detected per platform) |