debug: structured tool/HTTP logging, request IDs, config dump

Closes #13.

Today GITEA_DEBUG=true only flips the zap level to debug, dumps a
contextless `Text Result:` blob per tool call, and enables the gitea
SDK's own debug stream (which doesn't merge with our log file). That is
not enough to diagnose a misbehaving tool call in production.

This change introduces:

- A `pkg/middleware.ToolLogging` ToolHandlerMiddleware that logs each
  tool invocation on entry and exit with structured fields: tool name,
  redacted args, request_id, token source, duration_ms, and status. The
  request_id is stashed in the context so downstream layers can
  correlate.
- A `loggingRoundTripper` in `pkg/gitea` that wraps the shared HTTP
  transport and emits one structured line per upstream Gitea API call
  (method, token-stripped URL, status, duration_ms, bytes). This
  replaces — and is far more useful than — `gitea.SetDebugMode()`.
- An effective-config dump at startup (`logEffectiveConfig`) when
  debug+config scope is on, so "did my env var get picked up?" becomes
  answerable from the log file.
- Token source tracking. CLI flag / GITEA_ACCESS_TOKEN /
  GITEA_ACCESS_TOKEN_FILE / per-request Authorization header are now
  distinguished in logs as flag/env/env-file/header.
- A baseline redactor in `pkg/debug` that masks args / query params
  whose keys look like secrets (token, password, secret, api_key,
  authorization, …). This is the placeholder for issue #5's shared
  redactor; once that lands, callers here should defer to it.
- `GITEA_DEBUG_SCOPES` env var to scope debug output to any subset of
  `tools,http,config`. Default (unset) is "everything".

Test coverage was added for the redactor, scope flag, request-id
helpers, preview truncation (multibyte-safe), and the middleware's
context wiring + error propagation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pkg/gitea/transport.go

@@ -0,0 +1,67 @@
+package gitea
+
+import (
+	"net/http"
+	"time"
+
+	"gitea.com/gitea/gitea-mcp/pkg/debug"
+	"gitea.com/gitea/gitea-mcp/pkg/flag"
+	"gitea.com/gitea/gitea-mcp/pkg/log"
+
+	"go.uber.org/zap"
+)
+
+// loggingRoundTripper wraps an http.RoundTripper to emit one structured log
+// entry per upstream Gitea API call when debug is enabled. The information
+// here is much more useful for diagnosing slow / failing tool calls than the
+// gitea SDK's built-in debug mode (which only writes a separate, free-form
+// stream that doesn't merge with the zap log file).
+//
+// We log:
+//   - method, URL (with sensitive query params stripped)
+//   - request_id from the request context (when the caller propagated one)
+//   - HTTP status code (or transport-level error)
+//   - duration in milliseconds
+//   - response Content-Length when the server provided one
+//
+// We deliberately do NOT log request or response bodies — those routinely
+// contain user secrets (tokens being created, webhook payloads, file
+// contents) and the log file is meant to be safe to share.
+type loggingRoundTripper struct {
+	base http.RoundTripper
+}
+
+func (rt *loggingRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	if !flag.DebugScopeEnabled("http") {
+		return rt.base.RoundTrip(req)
+	}
+
+	start := time.Now()
+	resp, err := rt.base.RoundTrip(req)
+	duration := time.Since(start)
+
+	fields := []zap.Field{
+		zap.String("method", req.Method),
+		zap.String("url", debug.StripQueryTokens(req.URL.String())),
+		zap.Int64("duration_ms", duration.Milliseconds()),
+	}
+	if reqID := debug.RequestIDFromContext(req.Context()); reqID != "" {
+		fields = append(fields, zap.String("request_id", reqID))
+	}
+	if toolName := debug.ToolNameFromContext(req.Context()); toolName != "" {
+		fields = append(fields, zap.String("tool", toolName))
+	}
+
+	if err != nil {
+		fields = append(fields, zap.String("error", err.Error()))
+		log.Debug("gitea http: transport error", fields...)
+		return resp, err
+	}
+
+	fields = append(fields,
+		zap.Int("status", resp.StatusCode),
+		zap.Int64("bytes_in", resp.ContentLength),
+	)
+	log.Debug("gitea http: response", fields...)
+	return resp, nil
+}