M1.6: Set up slog-based structured logging

[bjcorder]

Labels: type:feature, area:cli, priority:high,
status:blocked, milestone:M1, phase:1

Summary

Configure log/slog (Go 1.21+ stdlib) as the project-wide logger, with
JSON output by default and human-readable when --log-format=text.

Acceptance criteria

• internal/logging/logging.go exposes Setup(format, level string) *slog.Logger
• JSON handler is the default; text handler when format=text
• Level is configurable via the level string
• The configured logger is set as the default via
  slog.SetDefault()
• Logger is wired into the cobra root command's PersistentPreRunE
• Sample logs are emitted by stub subcommands to demonstrate the
  setup works

Implementation notes

Use only log/slog from the standard library — no third-party logging
libraries. Format the JSON to include time, level, msg, and any
structured fields.

Dependencies

Depends on: #5

Verification

./forkguard --log-format=text ingest 2>&1 | grep "not implemented"
./forkguard --log-format=json ingest 2>&1 | jq .level

---

[bjcorder]

Implemented in 6c4c9ee76afa.

Summary:

• Added internal/logging.Setup(format, level string) *slog.Logger using stdlib log/slog.
• Supports JSON by default, text output with --log-format=text, and debug/info/warn/error levels.
• Sets the configured logger as the process default with slog.SetDefault().
• Wired logger setup into the cobra root command's PersistentPreRunE.
• Added sample logs to stub subcommands and structured error logging in the CLI entry point.

Validation:

• go test ./internal/logging/... — passed
• go test ./... — passed
• ./forkguard --log-format=text ingest 2>&1 | grep "not implemented" — passed
• ./forkguard --log-format=json ingest 2>&1 | jq .level — passed

Notes / follow-ups:

• None

[bjcorder]

Implemented in PR #39: #39

Implementation commits:

• 6c4c9ee76afa — Set up slog-based structured logging

Validation:

• make generate — passed
• go build ./... — passed
• go vet ./... — passed
• go run github.com/golangci/golangci-lint/cmd/golangci-lint@v1.64.8 run ./... — passed
• go test ./... -race -coverprofile=coverage.out — passed
• ./forkguard init and ./forkguard ingest --upstream github.com/openssl/openssl with idempotency check — passed

Closure status:

• This issue is ready to close when the PR is merged.

Remaining notes:

• None