test(e2e): add axe-core accessibility fixture and smoke spec

Adds @axe-core/playwright with a shared fixture providing an `axe`
helper. New a11y.spec.ts runs WCAG 2.1 AA checks on signin, dashboard,
timeline, allocations, resources, and projects pages. Currently reports
violations as warnings — upgrade to hard failures after fixes.

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

pnpm-lock.yaml

@@ -147,6 +147,9 @@ importers:
         specifier: ^3.23.8
         version: 3.25.76
     devDependencies:
+      '@axe-core/playwright':
+        specifier: ^4.11.1
+        version: 4.11.1(playwright-core@1.58.2)
       '@capakraken/eslint-config':
         specifier: workspace:*
         version: link:../../tooling/eslint
@@ -461,6 +464,11 @@ packages:
       nodemailer:
         optional: true
 
+  '@axe-core/playwright@4.11.1':
+    resolution: {integrity: sha512-mKEfoUIB1MkVTht0BGZFXtSAEKXMJoDkyV5YZ9jbBmZCcWDz71tegNsdTkIN8zc/yMi5Gm2kx7Z5YQ9PfWNAWw==}
+    peerDependencies:
+      playwright-core: '>= 1.0.0'
+
   '@babel/code-frame@7.29.0':
     resolution: {integrity: sha512-9NhCeYjq9+3uxgdtp20LSiJXJvN0FeCtNGpJxuMFZ1Kv3cWUNb6DOhJwUvcVCzKGR66cw4njwM6hrJLqgOwbcw==}
     engines: {node: '>=6.9.0'}
@@ -5453,6 +5461,11 @@ snapshots:
       preact: 10.24.3
       preact-render-to-string: 6.5.11(preact@10.24.3)
 
+  '@axe-core/playwright@4.11.1(playwright-core@1.58.2)':
+    dependencies:
+      axe-core: 4.11.2
+      playwright-core: 1.58.2
+
   '@babel/code-frame@7.29.0':
     dependencies:
       '@babel/helper-validator-identifier': 7.28.5