feat(metrics): Record analyze runs to SQLite

[TobiasGleiter]

Summary

Record every gogantic analyze run to a local SQLite database.
This data serves as the ground truth for before/after PR cycle metrics.

Schema

CREATE TABLE analyze_runs (
id INTEGER PRIMARY KEY AUTOINCREMENT,
repo_path TEXT NOT NULL,
run_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
files_read INTEGER,
issues_found INTEGER
);

Requirements

• Insert a row on every successful gogantic analyze run
• DB file location: ~/.gogantic/metrics.db
• Create the DB and table if they don't exist on first run
• repo_path should be the absolute path of the analyzed repo

Out of Scope

• The metrics report command (separate issue)
• GitHub API integration (separate issue)
• Failed/canceled analyze runs