ui: remove duplicate page headers

[TerrifiedBug]

Removes duplicate page headers, only relying on the side bar for navigation context.

[greptile-apps]

Greptile Summary

This PR removes the PageHeader component (which rendered an <h1> title and optional action row) from all 10 dashboard pages, delegating navigation context entirely to the sidebar. For pages that previously passed action buttons via the actions prop, those controls are preserved in a simple <div className="flex items-center justify-end"> wrapper.

• All 10 pages correctly drop the PageHeader import and its JSX usage
• Action CTAs (New Pipeline, New Environment, Add Rule, New Shared Component) are fully preserved in equivalent inline containers
• The PageHeader component itself (src/components/page-header.tsx) is not deleted by this PR — it now has no callers in the dashboard and could be removed in a follow-up cleanup
• No logic, data fetching, or security-sensitive code is touched; the change is purely presentational

Confidence Score: 5/5

• This PR is safe to merge — it is a pure UI simplification with no logic, data, or security changes.
• All changes are mechanical removals of a display-only component. Action buttons are correctly preserved. No data fetching, routing, auth, or state management is affected.
• No files require special attention. Consider a follow-up to delete the now-unused src/components/page-header.tsx.

Important Files Changed

Filename	Overview
src/app/(dashboard)/alerts/page.tsx	Removes PageHeader with title "Alerts"; preserves the "Add Rule" CTA button in a flex-end container.
src/app/(dashboard)/analytics/page.tsx	Removes PageHeader from both the empty-state early return and the main render path; preserves time-range toggle buttons in a flex-end wrapper.
src/app/(dashboard)/audit/page.tsx	Removes standalone PageHeader with title "Audit Log"; no actions to migrate, straightforward removal.
src/app/(dashboard)/environments/page.tsx	Removes PageHeader with title "Environments"; preserves "New Environment" link-button in a flex-end wrapper.
src/app/(dashboard)/fleet/page.tsx	Removes standalone PageHeader with title "Fleet"; no actions to migrate.
src/app/(dashboard)/library/shared-components/page.tsx	Removes PageHeader from both the empty-state and main render paths; preserves "New Shared Component" button in a flex-end wrapper.
src/app/(dashboard)/library/templates/page.tsx	Removes standalone PageHeader with title "Templates"; no actions to migrate.
src/app/(dashboard)/page.tsx	Removes standalone PageHeader with title "Dashboard"; no actions to migrate, tab bar immediately follows.
src/app/(dashboard)/pipelines/page.tsx	Removes PageHeader with title "Pipelines"; preserves "New Pipeline" link-button in a flex-end wrapper.
src/app/(dashboard)/profile/page.tsx	Removes standalone PageHeader with title "Profile"; no actions to migrate.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    subgraph Before["Before (each dashboard page)"]
        B1["<div className='space-y-*'>"]
        B2["<PageHeader title='...' actions={CTA} />\n(renders h1 + action row)"]
        B3["Page content"]
        B1 --> B2 --> B3
    end

    subgraph After["After (each dashboard page)"]
        A1["<div className='space-y-*'>"]
        A2["<div className='flex items-center justify-end'>\n  CTA button (if any)\n</div>"]
        A3["Page content"]
        A1 --> A2 --> A3
    end

    subgraph Sidebar["Sidebar (unchanged)"]
        S1["Active nav item\nprovides page context"]
    end

    Sidebar -.->|"now sole source of\npage title context"| After

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_{Last reviewed commit: 18b67f7}