fix(install): Copy embedded formulas to new installations

When `gt install` creates a new HQ, formulas were not being provisioned
to `.beads/formulas/`. This embeds the formula library into the gt binary
and copies them during installation.

- Add go:generate directive to copy formulas from .beads/formulas/
- Add internal/formula/embed.go with ProvisionFormulas() function
- Call ProvisionFormulas() from runInstall() after beads init
- Add generate target to Makefile (build depends on it)
- Add TestInstallFormulasProvisioned integration test
- Log warning if formula stat fails with unexpected error

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build install clean test
+.PHONY: build install clean test generate
 
 BINARY := gt
 BUILD_DIR := .
@@ -12,7 +12,10 @@ LDFLAGS := -X github.com/steveyegge/gastown/internal/cmd.Version=$(VERSION) \
            -X github.com/steveyegge/gastown/internal/cmd.Commit=$(COMMIT) \
            -X github.com/steveyegge/gastown/internal/cmd.BuildTime=$(BUILD_TIME)
 
-build:
+generate:
+	go generate ./...
+
+build: generate
 	go build -ldflags "$(LDFLAGS)" -o $(BUILD_DIR)/$(BINARY) ./cmd/gt
 ifeq ($(shell uname),Darwin)
 	@codesign -s - -f $(BUILD_DIR)/$(BINARY) 2>/dev/null || true