Defaults the Graph sidebar to unpinned and removes the Pro badge from the header

[sergeibbb]

Closes #5447 (part of #5391 — turning the Graph into the main GitLens panel)

Changes

• Defaults the Commit Graph sidebar to unpinned — flips the gitlens.graph.sidebar.pinned default to false (package.json + all fallbacks in graphWebview.ts, graph-app.ts, sidebar-panel.ts), so the sidebar floats over the graph in overlay mode and auto-collapses on focus loss. Users who explicitly set the setting are unaffected.
• Removes the Pro feature badge from the Graph header titlebar — the Start New menu (landed in 46bef5e) already provides the start-work entry point there. The badge in the feature gate (gate.ts) is intentionally untouched (gate redesign is a separate Explore consolidating views #5391 checklist item).
• CHANGELOG entries under [Unreleased] for both.

Note on placement: Start New is kept in its current slot (left of the Launchpad indicator) rather than moved into the badge's old rightmost slot — Trevor's "Replace 'Pro' badge with start work" is ambiguous on position; happy to swap if preferred (screenshots comparing both are available).

Verification

• pnpm run check passes
• Live-verified on a fresh profile: sidebarPinned resolves to false, the sidebar split-panel renders in overlay mode (graph keeps full width beneath the floating panel), and clicking back into the graph auto-collapses the open panel
• E2E: the two Pro-badge tests in graphHeader.test.ts were rewritten into one ("badge absent even on trial, Start New present") — passes
• E2E full suite: 6 failures (graphDetails compare panel, graphHeader Launchpad indicator, graphHeaderGitActions fetch popover, graphPin, graphReview branch-row chip, rebase keyboard shortcuts) — verified pre-existing: the identical set fails on bare origin/main (6dc193f) in a clean worktree. CI currently skips the E2E job, so these have gone unnoticed.

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