Replace raw <button> elements with TlaButton in the dotcom client

Part of #9189.

The dotcom client renders raw <button> elements in ~20 user-facing spots that should use TlaButton (or TldrawUiButton where a tldraw-UI button fits). Raw buttons miss the focus ring, disabled handling, variant styling, and consistent sizing that the shared component provides, and they force per-site CSS to re-create that behavior.

For contrast, the app already uses <TlaButton> in ~20 places — so about half of all buttons bypass the component.

Canonical component

• apps/dotcom/client/src/tla/components/TlaButton/TlaButton.tsx — variants primary, secondary, warning, cta
• packages/tldraw/src/lib/ui/components/primitives/Button/TldrawUiButton.tsx — for tldraw-UI contexts

Violation sites

• components/BoardHistoryLog/BoardHistoryLog.tsx:72
• components/StoreErrorScreen.tsx:27
• components/ErrorPage/ErrorPage.tsx:84
• tla/providers/TlaRootProviders.tsx:289
• tla/components/TlaSidebar/TlaSidebar.tsx:53
• tla/components/TlaSidebar/components/TlaSidebarFeedbackButton.tsx:16
• tla/components/TlaSidebar/components/TlaSidebarWorkspaceSwitcher.tsx:73, 135, 263
• tla/components/dialogs/WorkspaceSettingsDialog.tsx:382, 387
• tla/components/dialogs/TlaInviteDialog.tsx:48, 62
• tla/components/dialogs/TlaCookieConsent.tsx:112, 119, 125
• tla/components/TlaEditor/TlaEditorTopLeftPanel.tsx:128, 359
• tla/components/dialogs/TlaSignInDialog.tsx:470
• tla/pages/local-file-index.tsx:46

Out of scope

The raw <button> inside the primitives themselves is correct and should be left alone: TlaButton.tsx, TlaCtaButton.tsx (see #9189), and tla-menu.tsx. That is where the abstraction bottoms out.

Notes

• Some sites also carry ad-hoc button CSS classes (.acceptButton, .declineButton, .cookieButton, .inlineButton) — coordinate with the CSS consolidation sweep so the markup and styles move together.
• TlaEditorTopLeftPanel.tsx:128 is a width-setter element used for measurement, not a real action button; confirm whether it should stay a bare element before converting.

Acceptance

• Listed sites use TlaButton/TldrawUiButton with appropriate variants.
• No visual or behavior regressions in the affected dialogs, sidebar, and error screens.