feat(vscode): refactor provider form UX and route chat to secondary sidebar

[shatakshiiii]

Summary

• Refactor the add/edit provider form from an inline accordion to a native <dialog> modal with clear titles ("Add New Provider" / "Edit Provider: {name}"), fixing the below-the-fold discoverability issue
• Move the chat view from the left activity bar to the secondary sidebar (right side) using the secondarySidebar contribution point, matching the IDE convention for chat interfaces
• Add cross-navigation between provider panel and chat: "Start Chatting" button, gear menu in chat toolbar ("Configure Providers" / "Open Dashboard").
• Route "Start Chatting" to the native IDE chat (workbench.action.chat.open) with Abbenay as fallback — chat provider configuration is left to the consumer extension (e.g. vscode-ansible) to avoid duplicate settings
• Record the design rationale in docs/decisions.md (DR-045)
• Address webview UX findings from the Abbenay demo review
• JIRA: https://redhat.atlassian.net/browse/AAP-80494

Test plan

• npm run lint passes locally (0 errors)
• npm test — daemon 784/784 passed
• tsc --noEmit and esbuild pass for the vscode package
• Manual: verify "+ Add Provider" button appears above the provider list
• Manual: click "+ Add Provider" → modal opens with "Add New Provider" title
• Manual: click edit on a provider → modal opens with "Edit Provider: {name}" title
• Manual: verify chat view appears in the secondary sidebar (right side)
• Manual: verify "Start Chatting" opens native IDE chat (Copilot/Cursor), not Abbenay
• Manual: verify gear menu in chat toolbar opens with "Configure Providers" and "Open Dashboard"
• Manual: verify gear and dashboard icons appear in the chat view title bar