feat: add GitHub and GitLab webhook support (#170)

## Summary

Adds GitHub and GitLab push webhook support alongside the existing Gitea support.

closes #68

## What Changed

### Auto-detection of webhook source

The webhook handler now auto-detects which platform sent the webhook by examining HTTP headers:
- **Gitea**: `X-Gitea-Event`
- **GitHub**: `X-GitHub-Event`
- **GitLab**: `X-Gitlab-Event`

Existing Gitea webhooks continue to work unchanged. Unknown sources fall back to Gitea format for backward compatibility.

### Normalized push event

All three payload formats are parsed into a unified `PushEvent` struct containing:
- Source platform, ref, branch, commit SHA
- Repository name, clone URL, HTML URL
- Commit URL (with per-platform fallback logic)
- Pusher username/name

### New files

- **`internal/service/webhook/payloads.go`**: Source-specific payload structs (`GiteaPushPayload`, `GitHubPushPayload`, `GitLabPushPayload`), `ParsePushPayload()` dispatcher, per-platform parsers, branch extraction, and commit URL extraction functions.

### Modified files

- **`internal/service/webhook/types.go`**: Added `Source` type (gitea/github/gitlab/unknown), `DetectWebhookSource()`, `DetectEventType()`, and `PushEvent` normalized type. Moved `GiteaPushPayload` to payloads.go.
- **`internal/service/webhook/webhook.go`**: `HandleWebhook` now accepts a `Source` parameter and uses `ParsePushPayload()` for unified parsing instead of directly unmarshaling Gitea payloads.
- **`internal/handlers/webhook.go`**: Calls `DetectWebhookSource()` and `DetectEventType()` to auto-detect the platform before delegating to the webhook service.
- **`internal/service/webhook/webhook_test.go`**: Comprehensive tests for source detection, event type extraction, payload parsing (all 3 platforms), commit URL fallback paths, and integration tests through `HandleWebhook` for GitHub and GitLab sources.
- **`README.md`**: Updated description, features, non-goals, and architecture to reflect multi-platform webhook support.

## Test coverage

Webhook package: **96.9%** statement coverage. Tests cover:
- `DetectWebhookSource` with all header combinations and precedence
- `DetectEventType` for each platform
- `ParsePushPayload` for Gitea, GitHub, GitLab, unknown source, invalid JSON, empty payloads
- Commit URL extraction fallback paths for GitHub and GitLab
- Direct struct deserialization for all three payload types
- Full `HandleWebhook` integration tests with GitHub and GitLab sources

Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: #170
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/service/webhook/webhook.go

@@ -4,7 +4,6 @@ package webhook
 import (
 	"context"
 	"database/sql"
-	"encoding/json"
 	"fmt"
 	"log/slog"
 
@@ -44,68 +43,46 @@ func New(_ fx.Lifecycle, params ServiceParams) (*Service, error) {
 	}, nil
 }
 
-// GiteaPushPayload represents a Gitea push webhook payload.
-//
-//nolint:tagliatelle // Field names match Gitea API (snake_case)
-type GiteaPushPayload struct {
-	Ref        string      `json:"ref"`
-	Before     string      `json:"before"`
-	After      string      `json:"after"`
-	CompareURL UnparsedURL `json:"compare_url"`
-	Repository struct {
-		FullName string      `json:"full_name"`
-		CloneURL UnparsedURL `json:"clone_url"`
-		SSHURL   string      `json:"ssh_url"`
-		HTMLURL  UnparsedURL `json:"html_url"`
-	} `json:"repository"`
-	Pusher struct {
-		Username string `json:"username"`
-		Email    string `json:"email"`
-	} `json:"pusher"`
-	Commits []struct {
-		ID      string      `json:"id"`
-		URL     UnparsedURL `json:"url"`
-		Message string      `json:"message"`
-		Author  struct {
-			Name  string `json:"name"`
-			Email string `json:"email"`
-		} `json:"author"`
-	} `json:"commits"`
-}
-
-// HandleWebhook processes a webhook request.
+// HandleWebhook processes a webhook request from any supported source
+// (Gitea, GitHub, or GitLab). The source parameter determines which
+// payload format to use for parsing.
 func (svc *Service) HandleWebhook(
 	ctx context.Context,
 	app *models.App,
+	source Source,
 	eventType string,
 	payload []byte,
 ) error {
-	svc.log.Info("processing webhook", "app", app.Name, "event", eventType)
+	svc.log.Info("processing webhook",
+		"app", app.Name,
+		"source", source.String(),
+		"event", eventType,
+	)
 
-	// Parse payload
-	var pushPayload GiteaPushPayload
-
-	unmarshalErr := json.Unmarshal(payload, &pushPayload)
-	if unmarshalErr != nil {
-		svc.log.Warn("failed to parse webhook payload", "error", unmarshalErr)
-		// Continue anyway to log the event
+	// Parse payload into normalized push event
+	pushEvent, parseErr := ParsePushPayload(source, payload)
+	if parseErr != nil {
+		svc.log.Warn("failed to parse webhook payload",
+			"error", parseErr,
+			"source", source.String(),
+		)
+		// Continue with empty push event to still log the webhook
+		pushEvent = &PushEvent{Source: source}
 	}
 
-	// Extract branch from ref
-	branch := extractBranch(pushPayload.Ref)
-	commitSHA := pushPayload.After
-	commitURL := extractCommitURL(pushPayload)
-
 	// Check if branch matches
-	matched := branch == app.Branch
+	matched := pushEvent.Branch == app.Branch
 
 	// Create webhook event record
 	event := models.NewWebhookEvent(svc.db)
 	event.AppID = app.ID
 	event.EventType = eventType
-	event.Branch = branch
-	event.CommitSHA = sql.NullString{String: commitSHA, Valid: commitSHA != ""}
-	event.CommitURL = sql.NullString{String: commitURL.String(), Valid: commitURL != ""}
+	event.Branch = pushEvent.Branch
+	event.CommitSHA = sql.NullString{String: pushEvent.After, Valid: pushEvent.After != ""}
+	event.CommitURL = sql.NullString{
+		String: pushEvent.CommitURL.String(),
+		Valid:  pushEvent.CommitURL != "",
+	}
 	event.Payload = sql.NullString{String: string(payload), Valid: true}
 	event.Matched = matched
 	event.Processed = false
@@ -117,9 +94,10 @@ func (svc *Service) HandleWebhook(
 
 	svc.log.Info("webhook event recorded",
 		"app", app.Name,
-		"branch", branch,
+		"source", source.String(),
+		"branch", pushEvent.Branch,
 		"matched", matched,
-		"commit", commitSHA,
+		"commit", pushEvent.After,
 	)
 
 	// If branch matches, trigger deployment
@@ -154,33 +132,3 @@ func (svc *Service) triggerDeployment(
 		_ = event.Save(deployCtx)
 	}()
 }
-
-// extractBranch extracts the branch name from a git ref.
-func extractBranch(ref string) string {
-	// refs/heads/main -> main
-	const prefix = "refs/heads/"
-
-	if len(ref) >= len(prefix) && ref[:len(prefix)] == prefix {
-		return ref[len(prefix):]
-	}
-
-	return ref
-}
-
-// extractCommitURL extracts the commit URL from the webhook payload.
-// Prefers the URL from the head commit, falls back to constructing from repo URL.
-func extractCommitURL(payload GiteaPushPayload) UnparsedURL {
-	// Try to find the URL from the head commit (matching After SHA)
-	for _, commit := range payload.Commits {
-		if commit.ID == payload.After && commit.URL != "" {
-			return commit.URL
-		}
-	}
-
-	// Fall back to constructing URL from repo HTML URL
-	if payload.Repository.HTMLURL != "" && payload.After != "" {
-		return UnparsedURL(payload.Repository.HTMLURL.String() + "/commit/" + payload.After)
-	}
-
-	return ""
-}