feat(core-eslint): add pii-declaration-must-be-complete rule

Adds the `conformance/pii-declaration-must-be-complete` ESLint rule at
warn severity. The rule detects `custom: { pii: { ... } }` blocks in
Payload config files and warns when any of the four required sub-fields
(`category`, `purpose`, `exportable`, `restrictable`) is missing.

Incomplete PII declarations can produce incorrect audit reports —
sub-second editor feedback catches the gap before it reaches
compliance/data-map.yml.

- Rule + 7 RuleTester fixtures (complete passes, each missing field
  warns, non-pii custom block is no-op, malformed custom.pii is no-op)
- Registered in plugin.js + base.js at "warn"
- Conformance rule count bumped 7 → 8 in CLAUDE.md +
  conformance-quickref.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -696,6 +696,9 @@ importers:
       "@types/node":
         specifier: ^22.0.0
         version: 22.19.17
+      "@vitest/coverage-v8":
+        specifier: ^3.2.4
+        version: 3.2.4(vitest@3.2.4(@types/debug@4.1.13)(@types/node@22.19.17)(happy-dom@20.8.9)(jiti@2.6.1)(jsdom@25.0.1)(lightningcss@1.32.0)(sass@1.99.0)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))
       inversify:
         specifier: ^6.2.0
         version: 6.2.2(reflect-metadata@0.2.2)