fix(ui): search scrolling, filter layout, nav grouping, syllabus feedback history

[noor-lpi]

Description

Four UX fixes, one commit each:

1. Filters (Search + Chat)
   • Sections reordered: Sources → SDGs → Languages (panel and selected-filter pills).
   • Removed the source search box.
   • Each source category row now has its own checkbox to select/deselect all its sources, with a partial state (dash) and an x/y count. It works even when the category is folded.
   • The fold chevron moved to the right of the row, and sources are indented under their category.
   • Checkboxes are slightly smaller app-wide.
2. Search scrolling
   • Results now get the full column instead of a small inner scroll box.
   • Scrolling down collapses the search box into a one-line bar showing the query; clicking it (or scrolling back to the top) expands it.
   • Results always sit below the bar, never behind it, and there's no flicker.
   • On mobile/tablet the search column fills the screen, with the filters below.
3. Navigation
   • Tools on the left (Chat, Syllabus, Micro-learning, Search).
   • Utilities on the right, behind a divider (Bookmarks, Help, language), with consistent icon sizes and alignment.
   • About moved to the footer next to Terms.
   • More space after the logo.
4. Syllabus feedback history
   • Feedback already sent to the model is listed above the feedback box ("Changes you already requested (n)").
   • The list is cleared on restart and is kept for the session only.

Also fixed along the way:

• Help button: was disabled when a page was loaded or refreshed directly; it now works on first load.
• Syllabus feedback: the text was wiped even when sending failed; it's now kept so the user can retry.

Why?

• Search: results were hard to browse (about one card visible at a time).
• Filters: the order was illogical and selecting a whole source type took many clicks.
• Nav: it mixed features, personal pages and info pages in one row.
• Syllabus: users couldn't see what they had already asked the model to change.

How?

• Tested in the browser (Chrome) against the dev backend with real search/chat results, at desktop and mobile widths:
  • Search scroll, collapse and expand.
  • Filter select-all: all, none and partial states, including on folded categories.
  • Nav layout.
  • Syllabus feedback history, including a failed send.
• npm run test:unit: 31/31 pass (QandA snapshot updated for the new filter markup).
• Lint and Prettier clean.
• type-check reports no new errors (existing errors on main are unchanged).
• All new copy is in both EN and FR.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change

Checklist:

• My code follows the code style of this project.
• My code is tested.
• I have updated the documentation accordingly.

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