feat(filter-ui): Add filters bar, help modal, and better tooltips

[maddada]

Hey there,

This is another separate feature PR which adds the following filters bar to the app.

Closes #44 and #113

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Full user facing requirements (generated by Codex 5.4 high based on the plan I worked on with it):

• The files-tab search area now has a Filters toggle button on the right side of the main search bar. Clicking it or hides a secondary filter bar below the search input without changing the current query.

• The filter bar appears only on the files tab.

• The filter bar is visually grouped with separators between filter categories.

• The filter controls are:

  • In Folder
  • Parent Folder
  • No Subfolders
  • Kind
  • Type
  • Extension
  • Date
  • Size
  • Regex Example
  • a right-aligned Info button

• The In Folder, Parent Folder, and No Subfolders controls open a folder picker and insert the selected folder
  into the query using the corresponding search filter syntax.

• The non-path filters use dropdowns where that interaction makes sense.

• The Regex Example control appends a fixed example regex filter to the query.

• The toolbar edits the existing search query directly rather than maintaining a separate filter state.

• Filter behavior is query-aware:

  • ext: selections merge into a single extension filter such as ext:pdf;md
  • mutually exclusive filter families like kind, type, date, size, and folder scope replace only the existing from that same family
  • when a filter is replaced or merged, it stays in its existing position in the search input instead of being moved to the end
  • new filters append when there is no existing filter of that family

• The filter controls were normalized visually:

  • dropdowns and fixed-width filter buttons use the same width
  • the width is 90px
  • scope and regex button labels are left-aligned
  • dropdowns use a text caret ▼ instead of the previous SVG/background arrow
  • the dropdown caret remains visible on hover and is vertically centered

• The Info button is part of the filter bar, not the search input row, and is always right-aligned at the end of the last wrapped row.

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Search Help Modal

• Clicking Info opens a dedicated search help modal.
• The modal is focused on file search syntax only.
• The modal layout is organized with:
  • examples first at the top
  • one consolidated guide section below for the rest of the syntax explanation
• Example chips are interactive:
  • clicking an example copies/applies that example into the search input immediately
  • hovering an example shows a tooltip describing what that example demonstrates
• The help copy explicitly explains what gets matched, such as full file paths, folder paths, path segments, type/ filters, scope filters, date filters, size filters, regex, and content matching.
• The modal includes a button to open the Full Search Docs on GitHub.

[maddada]

@ldm0 Also implemented this feature because I need it, checked the code and it all looks good to me. I modified some of the styling by hand to make it better. Used Codex 5.4 high for the implementation but created a full plan before implementing and I believe the UX is perfect now. Please let me know what you think. It closes 2 issues (#44 and #113).