Remove the Go reference server; keep only Rust

The Go implementation is preserved in the v1.0.0 tag. Its observable
behaviour stays the API reference: responses recorded from the Go server
live in tools/compatibility_expected.txt, and tools/compatibility.py now
compares the Rust server against them (--update re-records after an
intentional change). The Go SQLite schema is frozen in
tests/fixtures/go_schema_v1.sql for the existing-database test.

Move the web client from internal/httpapi/web to web/, drop the Go CI job
and Go version pin, and update README, AGENTS.md and docs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/database/database.go

@@ -1,80 +0,0 @@
-package database
-
-import (
-	"context"
-	"database/sql"
-	"fmt"
-	"os"
-	"path/filepath"
-	"time"
-
-	_ "modernc.org/sqlite"
-)
-
-func Open(path string) (*sql.DB, error) {
-	directory := filepath.Dir(path)
-	if directory != "." {
-		if err := os.MkdirAll(directory, 0o750); err != nil {
-			return nil, fmt.Errorf("create database directory: %w", err)
-		}
-	}
-	db, err := sql.Open("sqlite", path+"?_pragma=foreign_keys(1)&_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)")
-	if err != nil {
-		return nil, err
-	}
-	db.SetMaxOpenConns(1)
-	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-	defer cancel()
-	if err := db.PingContext(ctx); err != nil {
-		_ = db.Close()
-		return nil, err
-	}
-	if err := migrate(ctx, db); err != nil {
-		_ = db.Close()
-		return nil, err
-	}
-	return db, nil
-}
-
-func migrate(ctx context.Context, db *sql.DB) error {
-	const schema = `
-CREATE TABLE IF NOT EXISTS users (
-  id TEXT PRIMARY KEY,
-  email TEXT NOT NULL UNIQUE COLLATE NOCASE,
-  password_hash TEXT NOT NULL,
-  created_at TEXT NOT NULL
-);
-CREATE TABLE IF NOT EXISTS refresh_tokens (
-  id INTEGER PRIMARY KEY AUTOINCREMENT,
-  token_hash TEXT NOT NULL UNIQUE,
-  user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  expires_at TEXT NOT NULL,
-  created_at TEXT NOT NULL,
-  revoked_at TEXT
-);
-CREATE INDEX IF NOT EXISTS refresh_tokens_user_idx ON refresh_tokens(user_id);
-CREATE TABLE IF NOT EXISTS records (
-  user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  entity TEXT NOT NULL,
-  record_id TEXT NOT NULL,
-  payload TEXT,
-  updated_at TEXT NOT NULL,
-  deleted INTEGER NOT NULL DEFAULT 0,
-  version INTEGER NOT NULL,
-  PRIMARY KEY (user_id, entity, record_id)
-);
-CREATE TABLE IF NOT EXISTS changes (
-  sequence INTEGER PRIMARY KEY AUTOINCREMENT,
-  user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  entity TEXT NOT NULL,
-  record_id TEXT NOT NULL,
-  payload TEXT,
-  updated_at TEXT NOT NULL,
-  deleted INTEGER NOT NULL,
-  version INTEGER NOT NULL
-);
-CREATE INDEX IF NOT EXISTS changes_user_sequence_idx ON changes(user_id, sequence);
-`
-	_, err := db.ExecContext(ctx, schema)
-	return err
-}