feat(cli): Implement complete command-line interface

Provides a user-friendly CLI for all GitLab Inbox operations.

src/cli/mod.rs - Clap command definitions:
- Global --config flag for alternate config path
- Subcommands: init, auth-test, doctor, version, backup, reset,
  migrate, sync-status, ingest, list, count, show
- Ingest supports --type (issues/merge_requests), --project filter,
  --force lock override, --full resync
- List supports rich filtering: --state, --author, --assignee,
  --label, --milestone, --since, --due-before, --has-due-date
- List supports --sort (updated/created/iid), --order (asc/desc)
- List supports --open to launch browser, --json for scripting

src/cli/commands/ - Command implementations:

init.rs: Interactive configuration wizard
- Prompts for GitLab URL, token env var, projects to track
- Creates config file and initializes database
- Supports --force overwrite and --non-interactive mode

auth_test.rs: Verify GitLab authentication
- Calls /api/v4/user to validate token
- Displays username and GitLab instance URL

doctor.rs: Environment health check
- Validates config file exists and parses correctly
- Checks database connectivity and migration state
- Verifies GitLab authentication
- Reports token environment variable status
- Supports --json output for CI integration

ingest.rs: Data synchronization from GitLab
- Acquires sync lock with stale detection
- Shows progress bars for issues and discussions
- Reports sync statistics on completion
- Supports --full flag to reset cursors and refetch all data

list.rs: Query local database
- Formatted table output with comfy-table
- Filters build dynamic SQL with parameterized queries
- Username filters normalize @ prefix automatically
- --open flag uses 'open' crate for cross-platform browser launch
- --json outputs array of issue objects

show.rs: Detailed entity view
- Displays issue metadata in structured format
- Shows full description with markdown
- Lists labels, assignees, milestone
- Shows discussion threads with notes

count.rs: Entity statistics
- Counts issues, discussions, or notes
- Supports --type filter for discussions/notes

sync_status.rs: Display sync watermarks
- Shows last sync time per project
- Displays cursor positions for debugging

src/main.rs - Application entry point:
- Initializes tracing subscriber with env-filter
- Parses CLI arguments via clap
- Dispatches to appropriate command handler
- Consistent error formatting for all failure modes

src/lib.rs - Library entry point:
- Exports cli, core, gitlab, ingestion modules
- Re-exports Config, GiError, Result for convenience

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cli/commands/auth_test.rs

@@ -0,0 +1,43 @@
+//! Auth test command - verify GitLab authentication.
+
+use crate::core::config::Config;
+use crate::core::error::{GiError, Result};
+use crate::gitlab::GitLabClient;
+
+/// Result of successful auth test.
+pub struct AuthTestResult {
+    pub username: String,
+    pub name: String,
+    pub base_url: String,
+}
+
+/// Run the auth-test command.
+pub async fn run_auth_test(config_path: Option<&str>) -> Result<AuthTestResult> {
+    // 1. Load config
+    let config = Config::load(config_path)?;
+
+    // 2. Get token from environment
+    let token = std::env::var(&config.gitlab.token_env_var)
+        .map(|t| t.trim().to_string())
+        .map_err(|_| GiError::TokenNotSet {
+            env_var: config.gitlab.token_env_var.clone(),
+        })?;
+
+    if token.is_empty() {
+        return Err(GiError::TokenNotSet {
+            env_var: config.gitlab.token_env_var.clone(),
+        });
+    }
+
+    // 3. Create client and test auth
+    let client = GitLabClient::new(&config.gitlab.base_url, &token, None);
+
+    // 4. Get current user
+    let user = client.get_current_user().await?;
+
+    Ok(AuthTestResult {
+        username: user.username,
+        name: user.name,
+        base_url: config.gitlab.base_url,
+    })
+}