Build every database's schema from embedded SQL files (closes #56)

The main database, each webhook's event database and each archive file
get their schema from SQL files under internal/db/migrations/, one
directory per kind. Opening a file runs, in one transaction, each file
that schema_migrations does not list. GORM stays for queries.
AutoMigrate is gone, tests included.

An event database holds only its own tables now, so the sweep that
removed target rows copied into it is deleted. The association guard
stays: without it a delivery write fails on the missing targets table.

AutoMigrate also had GORM parse every model before a handle was shared.
That is now done on its own: GORM races when two goroutines first use
models that refer to each other.

Model: opus-5-5

internal/db/migrations/events/000_migration.sql

@@ -0,0 +1,9 @@
+-- Migration 000: the table recording which migrations this file has
+-- had. Applied before the others; it records itself.
+
+CREATE TABLE IF NOT EXISTS schema_migrations (
+    version INTEGER PRIMARY KEY,
+    applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+
+INSERT OR IGNORE INTO schema_migrations (version) VALUES (0);

internal/db/migrations/events/001_schema.sql

@@ -0,0 +1,98 @@
+-- Migration 001: the schema of a webhook's event database. The models
+-- in internal/database must agree with it. The webhook, entrypoint and
+-- target ids here name rows in the main database, which has those
+-- tables; this file does not.
+
+CREATE TABLE events (
+    id uuid,
+    created_at datetime,
+    updated_at datetime,
+    deleted_at datetime,
+    webhook_id uuid NOT NULL,
+    entrypoint_id uuid NOT NULL,
+    method text NOT NULL,
+    raw_query text,
+    headers text,
+    body text,
+    content_type text,
+    body_bytes integer NOT NULL,
+    resubmitted_from_id uuid,
+    PRIMARY KEY (id)
+);
+
+CREATE INDEX idx_events_created_at ON events (created_at);
+CREATE INDEX idx_events_deleted_at ON events (deleted_at);
+CREATE INDEX idx_events_deleted_at_created_at
+    ON events (deleted_at, created_at);
+CREATE INDEX idx_events_resubmitted_from_id
+    ON events (resubmitted_from_id, deleted_at);
+CREATE INDEX idx_events_entrypoint_id
+    ON events (entrypoint_id, deleted_at, resubmitted_from_id, created_at);
+
+CREATE TABLE deliveries (
+    id uuid,
+    created_at datetime,
+    updated_at datetime,
+    deleted_at datetime,
+    event_id uuid NOT NULL,
+    target_id uuid NOT NULL,
+    status text NOT NULL DEFAULT 'pending',
+    finished_at datetime,
+    replay numeric NOT NULL DEFAULT false,
+    PRIMARY KEY (id),
+    CONSTRAINT fk_events_deliveries
+        FOREIGN KEY (event_id) REFERENCES events (id)
+);
+
+CREATE INDEX idx_deliveries_deleted_at ON deliveries (deleted_at);
+CREATE INDEX idx_deliveries_event_id ON deliveries (event_id, deleted_at);
+CREATE INDEX idx_deliveries_status
+    ON deliveries (status, deleted_at, finished_at, target_id);
+
+CREATE TABLE delivery_results (
+    id uuid,
+    created_at datetime,
+    updated_at datetime,
+    deleted_at datetime,
+    delivery_id uuid NOT NULL,
+    attempt_num integer NOT NULL,
+    success numeric,
+    status_code integer,
+    response_body text,
+    error text,
+    duration integer,
+    PRIMARY KEY (id),
+    CONSTRAINT fk_deliveries_delivery_results
+        FOREIGN KEY (delivery_id) REFERENCES deliveries (id)
+);
+
+CREATE INDEX idx_delivery_results_deleted_at
+    ON delivery_results (deleted_at);
+CREATE INDEX idx_delivery_results_delivery_id
+    ON delivery_results (delivery_id, deleted_at);
+
+CREATE TABLE event_totals (
+    id integer PRIMARY KEY AUTOINCREMENT,
+    events integer NOT NULL,
+    events_removed integer NOT NULL,
+    last_event_at datetime
+);
+
+-- The one row of event totals, all zero.
+INSERT INTO event_totals (events, events_removed) VALUES (0, 0);
+
+CREATE TABLE target_totals (
+    target_id uuid,
+    deliveries integer NOT NULL,
+    delivered integer NOT NULL,
+    failed integer NOT NULL,
+    deliveries_removed integer NOT NULL,
+    failed_removed integer NOT NULL,
+    PRIMARY KEY (target_id)
+);
+
+CREATE TABLE entrypoint_totals (
+    entrypoint_id uuid,
+    last_event_at datetime NOT NULL,
+    PRIMARY KEY (entrypoint_id)
+);