feat: architecture refactor — core layer, spreadsheet engine, envelope bidding, tests

- Add src/core/ (config, errors, events, http, observability, storage, query)
- Add src/Spreadsheet/ engine with native POI backend and Excel bridge
- Add Envelope C spreadsheet flow and tender bidding envelope modules
- Consolidate components into src/components/, remove legacy Component/ and Hooks/
- Add registration state/validation, auth session guard, profile edit modules
- Add unit tests across axios, redux, bidding, registration, encryption, core
- Add CI workflow, docs (architecture, audit, DSC API spec), keystore example
- Remove tracked keystore binary; ignore scripts.zip

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -36,6 +36,14 @@ local.properties
 !debug.keystore
 .kotlin/
 
+# Signing secrets — never commit keystores or their credentials
+android/app/appKeyStore
+android/keystore.properties
+keystore.properties
+
+# SonarQube scanner workspace
+.scannerwork/
+
 # node.js
 #
 node_modules/
@@ -81,3 +89,6 @@ rn-config-output.json
 !.yarn/releases
 !.yarn/sdks
 !.yarn/versions
+
+# Local archives
+scripts.zip