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.

web/templates/policies.html

@@ -0,0 +1,37 @@
+{{define "policies"}}{{template "base" .}}{{end}}
+{{define "title"}}Policy Rules — MCIAS{{end}}
+{{define "content"}}
+<div class="page-header d-flex align-center justify-between">
+  <div>
+    <h1>Policy Rules</h1>
+    <p class="text-muted text-small">{{len .Rules}} operator rules (built-in defaults not shown)</p>
+  </div>
+  <button class="btn btn-primary" onclick="document.getElementById('create-form').style.display='block';this.style.display='none'">
+    Add Rule
+  </button>
+</div>
+
+<div id="create-form" class="card mt-2" style="display:none">
+  <h2 style="font-size:1rem;font-weight:600;margin-bottom:1rem">Create Policy Rule</h2>
+  {{template "policy_form" .}}
+</div>
+
+<div class="table-wrapper mt-2">
+  <table>
+    <thead>
+      <tr>
+        <th>ID</th>
+        <th>Priority</th>
+        <th>Description</th>
+        <th>Effect</th>
+        <th>Enabled</th>
+        <th>Updated</th>
+        <th>Actions</th>
+      </tr>
+    </thead>
+    <tbody id="policies-tbody">
+      {{range .Rules}}{{template "policy_row" .}}{{end}}
+    </tbody>
+  </table>
+</div>
+{{end}}