Add PG creds + policy/tags UI; fix lint and build

- internal/ui/ui.go: add PGCred, Tags to AccountDetailData; register
  PUT /accounts/{id}/pgcreds and PUT /accounts/{id}/tags routes; add
  pgcreds_form.html and tags_editor.html to shared template set; remove
  unused AccountTagsData; fix fieldalignment on PolicyRuleView, PoliciesData
- internal/ui/handlers_accounts.go: add handleSetPGCreds — encrypts
  password via crypto.SealAESGCM, writes audit EventPGCredUpdated, renders
  pgcreds_form fragment; password never echoed; load PG creds and tags in
  handleAccountDetail
- internal/ui/handlers_policy.go: fix handleSetAccountTags to render with
  AccountDetailData instead of removed AccountTagsData
- internal/ui/ui_test.go: add 5 PG credential UI tests
- web/templates/fragments/pgcreds_form.html: new fragment — metadata display
  + set/replace form; system accounts only; password write-only
- web/templates/fragments/tags_editor.html: new fragment — textarea editor
  with HTMX PUT for atomic tag replacement
- web/templates/fragments/policy_form.html: rewrite to use structured fields
  matching handleCreatePolicyRule (roles/account_types/actions multi-select,
  resource_type, subject_uuid, service_names, required_tags, checkbox)
- web/templates/policies.html: new policies management page
- web/templates/fragments/policy_row.html: new HTMX table row with toggle
  and delete
- web/templates/account_detail.html: add Tags card and PG Credentials card
- web/templates/base.html: add Policies nav link
- internal/server/server.go: remove ~220 lines of duplicate tag/policy
  handler code (real implementations are in handlers_policy.go)
- internal/policy/engine_wrapper.go: fix corrupted source; use errors.New
- internal/db/policy_test.go: use model.AccountTypeHuman constant
- cmd/mciasctl/main.go: add nolint:gosec to int(os.Stdin.Fd()) calls
- gofmt/goimports: db/policy_test.go, policy/defaults.go,
  policy/engine_test.go, ui/ui.go, cmd/mciasctl/main.go
- fieldalignment: model.PolicyRuleRecord, policy.Engine, policy.Rule,
  policy.RuleBody, ui.PolicyRuleView
Security: PG password encrypted AES-256-GCM with fresh random nonce before
storage; plaintext never logged or returned in any response; audit event
written on every credential write.

internal/ui/handlers_accounts.go

@@ -143,6 +143,12 @@ func (u *UIServer) handleAccountDetail(w http.ResponseWriter, r *http.Request) {
 		// ErrNotFound is expected when no credentials have been stored yet.
 	}
 
+	tags, err := u.db.GetAccountTags(acct.ID)
+	if err != nil {
+		u.logger.Warn("get account tags", "error", err)
+		tags = nil
+	}
+
 	u.render(w, "account_detail", AccountDetailData{
 		PageData: PageData{CSRFToken: csrfToken},
 		Account:  acct,
@@ -150,6 +156,7 @@ func (u *UIServer) handleAccountDetail(w http.ResponseWriter, r *http.Request) {
 		AllRoles: knownRoles,
 		Tokens:   tokens,
 		PGCred:   pgCred,
+		Tags:     tags,
 	})
 }