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/model/model.go

@@ -131,4 +131,26 @@ const (
 	EventTOTPRemoved    = "totp_removed"
 	EventPGCredAccessed = "pgcred_accessed"
 	EventPGCredUpdated  = "pgcred_updated" //nolint:gosec // G101: audit event type string, not a credential
+
+	EventTagAdded   = "tag_added"
+	EventTagRemoved = "tag_removed"
+
+	EventPolicyRuleCreated = "policy_rule_created"
+	EventPolicyRuleUpdated = "policy_rule_updated"
+	EventPolicyRuleDeleted = "policy_rule_deleted"
+	EventPolicyDeny        = "policy_deny"
 )
+
+// PolicyRuleRecord is the database representation of a policy rule.
+// RuleJSON holds a JSON-encoded policy.RuleBody (all match and effect fields).
+// The ID, Priority, and Description are stored as dedicated columns.
+type PolicyRuleRecord struct {
+	CreatedAt   time.Time `json:"created_at"`
+	UpdatedAt   time.Time `json:"updated_at"`
+	CreatedBy   *int64    `json:"-"`
+	Description string    `json:"description"`
+	RuleJSON    string    `json:"rule_json"`
+	ID          int64     `json:"id"`
+	Priority    int       `json:"priority"`
+	Enabled     bool      `json:"enabled"`
+}