feat(week7): add Heka Web Wallet extension and contributor onboarding UI

Chrome Extension (heka-chrome-extension/):
- Manifest V3 Chrome extension: service worker, popup, and content script
- WebCrypto ECDSA P-256 non-extractable key pair in IndexedDB (key-store.ts)
- did:jwk DID derivation from holder public key (did.ts)
- SD-JWT VC credential store in chrome.storage.local (credential-store.ts)
- Full OID4VCI Pre-Authorized Code Flow (oid4vci/receive.ts):
  - Parses openid-credential-offer:// URIs (by-value and by-reference)
  - Fetches /.well-known/openid-credential-issuer metadata
  - Discovers token endpoint from issuer or authorization server metadata
  - Exchanges pre-authorized_code for an access token
  - Builds JWT proof of possession signed with holder's WebCrypto P-256 key
  - Requests and stores the resulting SD-JWT VC
- Background service worker: holder key generation on install, badge
  management, PING/RECEIVE_OFFER/GET_STATUS message routing (service-worker.ts)
- Content script bridge: source-tag-validated message forwarding from Heka
  web pages to the extension SW (heka-bridge.ts)
- Popup UI (React + inline styles, no Tailwind):
  - WalletStatus: displays holder DID (truncated, copyable), credential count
  - CredentialList: renders held SD-JWT VC cards with vct, issuer, date
  - ReceiveCredential: textarea + status feedback for the OID4VCI flow
  - App: tab navigation (Wallet / Receive), auto-opens Receive on pending URI

Web UI Contributor Onboarding (heka-identity-service-web-ui/):
- ContributorBinding Redux slice with typed async thunks and selectors
- 4-step onboarding wizard (ContributorOnboarding.tsx):
  - Step 0 GithubLoginStep: OAuth redirect via getGithubAuthorizationUrl
  - Step 1 ChallengeStep: requests GPG nonce from /v2/gpg-challenge/request
  - Step 2 SignStep: displays nonce, terminal command, signature textarea
  - Step 3 VerifyStep: submits signature, shows credential offer URI and QR
- ContributorHub page wired into the sidebar nav and app router
- GitHub OAuth callback handler (ContributorGithubCallback.tsx)
- Shared API error utility and endpoint constants

Depends on: feat/gpg-challenge-module (PR #184),
            feat/github-auth-contributor-binding (PR #186),
            feat/contributor-credential-issuance (PR #192)

Signed-off-by: darshit2308 <darshit2308@gmail.com>

Author: darshit2308

heka-chrome-extension/.gitignore

@@ -0,0 +1,7 @@
+# Build output — generated by `yarn build` / `yarn dev`
+dist/
+
+# Local dev cache
+node_modules/
+.yarn/cache
+.yarn/install-state.gz

heka-chrome-extension/icons/icon-128.png

@@ -0,0 +1,56 @@
+{
+  "manifest_version": 3,
+  "name": "Heka Web Wallet",
+  "version": "0.1.0",
+  "description": "Hiero contributor credential wallet — receive, store, and present your GithubContributorCredential.",
+
+  "permissions": [
+    "storage",
+    "alarms",
+    "notifications"
+  ],
+  "host_permissions": [
+    "https://*/*",
+    "http://localhost/*"
+  ],
+
+  "background": {
+    "service_worker": "background/service-worker.js",
+    "type": "module"
+  },
+
+  "action": {
+    "default_popup": "popup/index.html",
+    "default_title": "Heka Web Wallet",
+    "default_icon": {
+      "16":  "icons/icon-16.png",
+      "48":  "icons/icon-48.png",
+      "128": "icons/icon-128.png"
+    }
+  },
+
+  "content_scripts": [
+    {
+      "matches": [
+        "http://localhost/*",
+        "https://heka.hiero.org/*",
+        "https://*.hiero.org/*"
+      ],
+      "js":  ["content-scripts/heka-bridge.js"],
+      "run_at": "document_idle"
+    }
+  ],
+
+  "icons": {
+    "16":  "icons/icon-16.png",
+    "48":  "icons/icon-48.png",
+    "128": "icons/icon-128.png"
+  },
+
+  "protocol_handlers": [
+    {
+      "protocol": "openid-credential-offer",
+      "uriTemplate": "/popup/index.html?offer=%s"
+    }
+  ]
+}