feat: add coderm.titleBar.hideMoreActions to hide title bar overflow

[j4rviscmd]

Summary

• Adds Coderm-specific boolean setting coderm.titleBar.hideMoreActions (default: true) that hides the trailing "More Actions" (...) overflow button in the title bar.
• The button is contributed by WorkbenchToolBar's ToggleMenuAction whenever secondary actions exist (e.g. Copilot Chat's "Open in Agents" / "Chat"). It is suppressed via a body class + scoped CSS rule because the host's overflowBehavior repopulates secondary actions from primary regardless of what callers pass to setActions, so dropping the secondary argument from titlebarPart.ts has no effect.
• Implementation follows the established Coderm contribution pattern (compare cursorAutoHide.ts, activePaneBorder.ts): one new file under src/vs/workbench/contrib/coderm/browser/, side-effect import in coderm.contribution.ts, README sync for EN/JA. titlebarPart.ts is intentionally left untouched to minimize upstream-merge conflicts.

Test plan

• Build passes (npm run compile, 0 errors)
• compile-check-ts-native type check passes
• Default state (setting = true): the ... button is hidden in the title bar even with extensions that contribute secondary actions (Copilot Chat, etc.) installed
• Toggling the setting to false at runtime immediately restores the ... button (no reload required)
• Other title bar actions (layout toggles, accounts, notifications) remain visible in both states
• No accidental hiding of .codicon-toolbar-more in other toolbars (command center, activity bar, editor toolbar)

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