chore: add project tooling with Makefile, golangci-lint config, and CLAUDE.md

Establish the quality infrastructure for the cburn project:

- Makefile: standardized targets for build, install, lint, test, test-race,
  bench, and fuzz. Uses explicit Go path (/usr/local/go/bin/go) for
  reproducibility. Fuzz defaults to 30s with FUZZ_TIME override.

- .golangci.yml (v2 format): enables gosec (security), revive (style),
  gocritic (bugs/perf), errcheck, nilerr, perfsprint, prealloc, and
  standard static analysis. Disables noisy rules (exported doc requirement,
  ifElseChain, deferred .Close() gosec G104). Includes gofmt + goimports
  formatters.

- CLAUDE.md: comprehensive project guide covering architecture overview,
  data flow diagram, package map, build/test commands, key design decisions
  (byte-level parsing, mtime-based caching, async TUI loading), and
  configuration reference.

- .gitignore: add pipeline.test to ignored test artifacts.

Makefile

@@ -0,0 +1,34 @@
+GO := /usr/local/go/bin/go
+BIN := cburn
+
+.PHONY: build install lint test test-race bench fuzz clean
+
+## Build & install
+build:
+	$(GO) build -o $(BIN) .
+
+install:
+	$(GO) install .
+
+## Quality
+lint:
+	golangci-lint run ./...
+
+test:
+	$(GO) test ./...
+
+test-race:
+	$(GO) test -race ./...
+
+bench:
+	$(GO) test -bench=. -benchmem ./internal/pipeline/
+
+## Fuzz (run for 30s by default, override with FUZZ_TIME=2m)
+FUZZ_TIME ?= 30s
+fuzz:
+	$(GO) test -fuzz=Fuzz -fuzztime=$(FUZZ_TIME) ./internal/source/
+
+## Housekeeping
+clean:
+	rm -f $(BIN)
+	$(GO) clean -testcache