Implement Phase 0+1: project setup, config, database, migrations

- Go module, Makefile, .golangci.yaml, .gitignore, example config
- TOML config loading with validation
- SQLite database with WAL, foreign keys, busy timeout
- Schema migrations: users, webauthn_credentials, notebooks, pages,
  strokes, share_links with indexes and cascading deletes
- 4 tests: open+migrate, idempotent, foreign keys, cascade delete

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Makefile

@@ -0,0 +1,32 @@
+.PHONY: build test vet lint proto proto-lint clean all
+
+LDFLAGS := -trimpath -ldflags="-s -w -X main.version=$(shell git describe --tags --always --dirty 2>/dev/null || echo dev)"
+
+eng-pad-server:
+	CGO_ENABLED=0 go build $(LDFLAGS) -o eng-pad-server ./cmd/eng-pad-server
+
+build:
+	go build ./...
+
+test:
+	go test ./...
+
+vet:
+	go vet ./...
+
+lint:
+	golangci-lint run ./...
+
+proto:
+	protoc --go_out=. --go_opt=module=git.wntrmute.dev/kyle/eng-pad-server \
+		--go-grpc_out=. --go-grpc_opt=module=git.wntrmute.dev/kyle/eng-pad-server \
+		proto/engpad/v1/*.proto
+
+proto-lint:
+	buf lint
+	buf breaking --against '.git#branch=master,subdir=proto'
+
+clean:
+	rm -f eng-pad-server
+
+all: vet lint test eng-pad-server