guide: read-only guided manual-rotation layer (links + worklist + TUI)

Advances the guided-rotation goal without rotating anything.

- internal/links: offline change-password URL generation — curated per-service
  table + RFC 8615 /.well-known/change-password + parent-domain fallback; derives
  a web host from a credential (git/netrc "user @ host", docker registry, aws)
- internal/worklist: secrets-free rotation worklist (source, identity, auto/manual,
  link) + Markdown renderer
- internal/tui: Bubble Tea walk-through (one credential per screen, open link,
  mark done/skip, progress) — READ-ONLY, enters/stores no secret
- cmd: `incredigo worklist` (offline, stdout/--out) and `incredigo guide` (TUI)
- tests: link derivation, worklist build/markdown + no-secret-column, TUI
  navigation/done/quit/view

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/links/links_test.go

@@ -0,0 +1,56 @@
+package links
+
+import (
+	"testing"
+
+	"incredigo/internal/discover"
+)
+
+func TestFor(t *testing.T) {
+	cases := []struct {
+		host    string
+		wantURL string
+		wantSrc Source
+	}{
+		{"github.com", "https://github.com/settings/tokens", SourceKnown},
+		{"GitHub.com:443", "https://github.com/settings/tokens", SourceKnown},
+		{"api.github.com", "https://github.com/settings/tokens", SourceKnown}, // parent-domain fallback
+		{"s3.amazonaws.com", "https://console.aws.amazon.com/iam/home#/security_credentials", SourceKnown},
+		{"example.com", "https://example.com/.well-known/change-password", SourceWellKnown},
+		{"registry.internal.corp", "https://registry.internal.corp/.well-known/change-password", SourceWellKnown},
+		{"", "", SourceNone},
+	}
+	for _, c := range cases {
+		got := For(c.host)
+		if got.URL != c.wantURL || got.Source != c.wantSrc {
+			t.Errorf("For(%q) = {%q,%s}, want {%q,%s}", c.host, got.URL, got.Source, c.wantURL, c.wantSrc)
+		}
+	}
+}
+
+func TestHostFor(t *testing.T) {
+	cases := []struct {
+		cred discover.Credential
+		want string
+	}{
+		{discover.Credential{Source: "git", Identity: "alice @ github.com"}, "github.com"},
+		{discover.Credential{Source: "netrc", Identity: "bob @ api.example.com"}, "api.example.com"},
+		{discover.Credential{Source: "netrc", Identity: "bob @ default"}, ""}, // netrc "default" is not a host
+		{discover.Credential{Source: "docker", Identity: "ghcr.io"}, "ghcr.io"},
+		{discover.Credential{Source: "aws", Identity: "default / AKIA***"}, "console.aws.amazon.com"},
+		{discover.Credential{Source: "ssh", Identity: "id_ed25519"}, ""},
+		{discover.Credential{Source: "file", Identity: "keys/deploy"}, ""},
+	}
+	for _, c := range cases {
+		if got := HostFor(c.cred); got != c.want {
+			t.Errorf("HostFor(%s/%q) = %q, want %q", c.cred.Source, c.cred.Identity, got, c.want)
+		}
+	}
+}
+
+func TestLinkForGit(t *testing.T) {
+	l := LinkFor(discover.Credential{Source: "git", Identity: "alice @ github.com"})
+	if l.Source != SourceKnown || l.URL != "https://github.com/settings/tokens" {
+		t.Errorf("LinkFor git github = {%q,%s}", l.URL, l.Source)
+	}
+}