feat: show document title for Project detail pages

[blfpd]

Checklist

• This PR is not opened from my fork’s main branch

What This PR Implements

Show document.head title of Project detail pages

Fixes: #2090

Changes Made

• Add a +layout.svelte under /(app)/projects/

Testing Done

• Development environment started: ./scripts/development/dev.sh start
• Frontend verified at http://localhost:3000
• Backend verified at http://localhost:3552
• Manual testing completed (describe):
• No linting errors (e.g., just lint all)
• Backend tests pass: just test backend

AI Tool Used (if applicable)

no

Additional Context

See #2090

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Greptile Summary

This PR introduces a new +layout.svelte at the (app)/projects/ level to set a dynamic <svelte:head><title> for project pages, and adds a Playwright test asserting the title on the new-project page.

• Layout placement — placing the layout at (app)/projects/ causes it to wrap /projects (list), /projects/new, and /projects/[projectId] alike. On the list page page.data.project is always undefined, so the title permanently reads "Arcane | Projects | My New Project" (the placeholder), which is misleading.
• || vs ?? — page.data?.project?.name || m.compose_project_name_placeholder() treats an empty-string project name as falsy and falls back to the placeholder; ?? would be the correct operator here.
• Test scope — the new test ('should have a head title') lives in the New Compose Project Page describe block, which is always on /projects/new where page.data.project is undefined. The test will pass because it asserts the placeholder value, but it does not verify that the detail page (/projects/[projectId]) shows the actual project name — the stated goal of the PR.
• The $derived reactive declarations and {@render children()} usage are idiomatic Svelte 5 patterns.

Confidence Score: 3/5

• The PR achieves its goal on the detail page but introduces an unintended side-effect on the projects list page and lacks a meaningful title test for the detail page.
• The layout scope is broader than intended — /projects (list page) will permanently display the placeholder "My New Project" in the document title. The || operator also silently swallows empty-string project names. The new test passes but only validates the fallback path, leaving the detail-page title (the PR's stated goal) without coverage. These issues lower the confidence from an otherwise straightforward change.
• frontend/src/routes/(app)/projects/+layout.svelte — layout placement and || operator need attention.

Important Files Changed

Filename	Overview
frontend/src/routes/(app)/projects/+layout.svelte	Adds a shared layout that derives a <title> from page.data.project.name with a placeholder fallback; because it is placed at the (app)/projects/ level it applies to all three sub-routes (/projects, /projects/new, /projects/[projectId]), producing a misleading "My New Project" title on the projects list page, and uses `
tests/spec/project.spec.ts	Adds a title assertion test inside the "New Compose Project Page" describe block; the test correctly matches the placeholder fallback ("My New Project") and will pass, but it only validates the fallback behavior on /projects/new rather than an actual project name on the detail page, leaving the PR's primary goal untested.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Browser navigates to /projects/*] --> B{Which route?}
    B -->|/projects| C[page.data = projects, counts]
    B -->|/projects/new| D[page.data = templates, envTemplate]
    B -->|/projects/projectId| E[page.data = project, editorState]

    C --> F{page.data?.project?.name}
    D --> F
    E --> F

    F -->|undefined| G[Fallback: 'My New Project']
    F -->|empty string via OR| G
    F -->|real name| H[Use project.name]

    G --> I["Title: 'Arcane | Projects | My New Project'"]
    H --> J["Title: 'Arcane | Projects | actual-name'"]

    I -->|⚠️ misleading on /projects list| K[svelte:head title set]
    I -->|✓ correct on /projects/new| K
    J -->|✓ correct on detail page| K

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_{Last reviewed commit: b495010}

Context used:

• Rule used - What: Avoid updating $state inside $effect blo... (source)

[blfpd]

@greptileai Redo the review with current push-forced commit