feat: add GitHub repository dashboard with Prometheus metrics

ghtracker authenticates as a GitHub App and scans a configured list of repositories on a schedule. It serves a dashboard, a JSON state endpoint, a health probe and Prometheus metrics.

The dashboard lists only items that need attention: failing workflows, pull requests that wait too long or fail their checks, stale issues and projects that failed to scan. It has search, dynamic filters and a button that rescans on demand. The Vue app is embedded in the Go binary.

The client protects the GitHub rate limit with conditional requests, a request reserve and Retry-After handling.

internal/model/model.go

@@ -0,0 +1,146 @@
+// Package model holds the data shapes shared by the collector, metrics and web layers.
+package model
+
+import (
+	"errors"
+	"time"
+)
+
+// ErrRateLimited means GitHub limits were hit or are about to be; callers must stop issuing requests.
+var ErrRateLimited = errors.New("github rate limit reached")
+
+type Severity int
+
+const (
+	OK Severity = iota
+	Warn
+	Crit
+)
+
+func (s Severity) String() string {
+	switch s {
+	case Warn:
+		return "warn"
+	case Crit:
+		return "crit"
+	default:
+		return "ok"
+	}
+}
+
+type CheckState string
+
+const (
+	ChecksNone    CheckState = "none"
+	ChecksPending CheckState = "pending"
+	ChecksPass    CheckState = "success"
+	ChecksFail    CheckState = "failure"
+	ChecksUnknown CheckState = "unknown"
+)
+
+type Repo struct {
+	RefreshedAt   time.Time
+	Release       *Release
+	Description   string
+	FullName      string
+	DefaultBranch string
+	ReleasesURL   string
+	// Err is set when the last refresh failed entirely; the other fields hold the last good data.
+	Err       string
+	URL       string
+	Issues    []Issue
+	PRs       []PullRequest
+	Workflows []Workflow
+	// Warnings lists sections that failed to load while the rest succeeded.
+	Warnings []string
+	Health   Severity
+	Archived bool
+	Up       bool
+}
+
+type Release struct {
+	PublishedAt time.Time
+	Tag         string
+	Name        string
+	URL         string
+	Prerelease  bool
+	// FromTag marks a version taken from tags because the repo has no releases.
+	FromTag bool
+}
+
+type Issue struct {
+	CreatedAt time.Time
+	UpdatedAt time.Time
+	Title     string
+	URL       string
+	Author    string
+	Labels    []string
+	Number    int
+	Comments  int
+}
+
+type PullRequest struct {
+	CreatedAt time.Time
+	UpdatedAt time.Time
+	Title     string
+	URL       string
+	Author    string
+	HeadSHA   string
+	Labels    []string
+	Checks    CheckSummary
+	Number    int
+	Draft     bool
+}
+
+type CheckSummary struct {
+	State   CheckState
+	Failing []string
+	Total   int
+	Failed  int
+	Pending int
+}
+
+type Workflow struct {
+	// LastDone is the newest completed run; nil when no run has completed yet.
+	LastDone   *Run
+	Name       string
+	URL        string
+	Latest     Run
+	Background bool
+}
+
+type Run struct {
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+	URL        string
+	Event      string
+	Branch     string
+	Status     string
+	Conclusion string
+	ID         int64
+}
+
+// Running reports whether the run has not completed.
+func (r Run) Running() bool { return r.Status != "completed" }
+
+// Failed reports whether a completed run ended in a failing conclusion.
+func (r Run) Failed() bool {
+	switch r.Conclusion {
+	case "failure", "timed_out", "startup_failure", "action_required":
+		return true
+	}
+	return false
+}
+
+type Alert struct {
+	Since    time.Time
+	Repo     string
+	Kind     string
+	Subject  string
+	Detail   string
+	URL      string
+	Severity Severity
+}
+
+// Message renders the alert as one line for logs and the JSON API.
+func (a Alert) Message() string { return a.Subject + ": " + a.Detail }