Initial commit: project scaffold, full spec, database schema, bot and cron

- SPEC.md: full project specification from design discussion
- schema.sql: SQLite database schema
- db.py: database wrapper with all query functions
- bot.py: telegram bot entrypoint
- commands.py: all command handlers with admin/creator guards
- cron.py: daily reminder job
- requirements.txt: python-telegram-bot, dateparser
- README.md, CONTRIBUTING.md
- .gitignore

schema.sql

@@ -0,0 +1,49 @@
+-- JIGAIDO Database Schema
+
+CREATE TABLE IF NOT EXISTS groups (
+    id              INTEGER PRIMARY KEY AUTOINCREMENT,
+    telegram_chat_id INTEGER UNIQUE NOT NULL,
+    creator_user_id  INTEGER NOT NULL,
+    created_at       INTEGER NOT NULL DEFAULT (unixepoch())
+);
+
+CREATE TABLE IF NOT EXISTS group_admins (
+    group_id  INTEGER REFERENCES groups(id) ON DELETE CASCADE,
+    user_id   INTEGER NOT NULL,
+    PRIMARY KEY (group_id, user_id)
+);
+
+CREATE TABLE IF NOT EXISTS users (
+    id               INTEGER PRIMARY KEY AUTOINCREMENT,
+    telegram_user_id  INTEGER UNIQUE NOT NULL,
+    username          TEXT,
+    created_at        INTEGER NOT NULL DEFAULT (unixepoch())
+);
+
+CREATE TABLE IF NOT EXISTS bounties (
+    id                   INTEGER PRIMARY KEY AUTOINCREMENT,
+    group_id              INTEGER REFERENCES groups(id) ON DELETE CASCADE,
+    created_by_user_id    INTEGER REFERENCES users(id),
+    informed_by_username  TEXT NOT NULL,
+    text                  TEXT,
+    link                  TEXT,
+    due_date_ts           INTEGER,
+    created_at            INTEGER NOT NULL DEFAULT (unixepoch()),
+    UNIQUE(group_id, link)
+);
+
+CREATE TABLE IF NOT EXISTS user_bounty_tracking (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    bounty_id  INTEGER NOT NULL REFERENCES bounties(id) ON DELETE CASCADE,
+    added_at   INTEGER NOT NULL DEFAULT (unixepoch()),
+    UNIQUE(user_id, bounty_id)
+);
+
+CREATE TABLE IF NOT EXISTS reminder_log (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    bounty_id   INTEGER NOT NULL REFERENCES bounties(id) ON DELETE CASCADE,
+    reminded_at INTEGER NOT NULL DEFAULT (unixepoch()),
+    UNIQUE(user_id, bounty_id)
+);