replace logrus with log/slog across all packages (#1)

[Nicolas-Peiffer]

• replace logrus with log/slog across all packages

Migrate all logging calls from github.com/sirupsen/logrus to the standard library log/slog (Go 1.21+). Key changes:

• Add pkg/logging package with LevelTrace = slog.Level(-8) constant and ParseLevel helper shared across cmd and provider packages
• Add github.com/lmittmann/tint for colored text handler (replaces logrus text formatter with color support)
• Replace logrus-filename hook with slog.HandlerOptions{AddSource: true}
• Rename version.LogrusOutputVersion() to version.LogVersion()
• Accept log levels: trace, debug, info, warn, error, quiet (drop logrus-specific: warning, fatal, panic)
• logrus.Fatal → slog.Error + os.Exit(1)
• logrus.Trace/Tracef → slog.Log(ctx, logging.LevelTrace, ...)
• logrus.WithFields/WithField/WithError → inline slog key-value pairs
• Remove github.com/keepeye/logrus-filename from go.mod
• logrus remains only as an indirect dependency (pulled by other modules)

https://claude.ai/code/session_01BDmDyCyMiNjx4HMQwPWv7s

• Improve slog usage: structured args, snake_case keys, Fatal helper, LevelVar

• Add logging.Fatal helper (slog.Error + os.Exit(1)) to pkg/logging
• Add activeLogLevel (*slog.LevelVar) in root.go for runtime-adjustable level
• Replace all fmt.Sprintf inside slog calls with structured key-value args
• Fix slog.Error(err.Error()) anti-pattern throughout; pass err as "error" attr
• Fix nil-panic bug in istio.go GenerateDEK (err was nil when request==nil)
• Rename all log keys to snake_case: cobra-cmd→cobra_cmd, keyId→key_id, etc.
• Use real gRPC ctx instead of context.Background() in Encrypt method traces
• Replace slog.Error+os.Exit(1) patterns with logging.Fatal in serve/rotation/test
• Drop unused fmt and os imports where no longer needed

https://claude.ai/code/session_01BDmDyCyMiNjx4HMQwPWv7s

• Update copyright year to 2026 in modified files

https://claude.ai/code/session_01BDmDyCyMiNjx4HMQwPWv7s

• logging: add quiet level that discards all output

Introduce logging.LevelQuiet (slog.Level(math.MaxInt)) and wire it up so that --log-level=quiet installs slog.DiscardHandler, producing no log output at all.

• pkg/logging: add LevelQuiet constant, "quiet" case in ParseLevel
• cmd/root.go: detect LevelQuiet in initConfig and short-circuit with slog.DiscardHandler; update --log-level flag description and shell completion to include "quiet"

https://claude.ai/code/session_01BDmDyCyMiNjx4HMQwPWv7s

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Proposed Changes

Types of Changes

Verification

Testing

Linked Issues

#48

User-Facing Change

Further Comments

gose and crypto11 will soon replace logrus by log/slog.