feat(tui): add interactive file type filtering via T key

[ShivamB25]

Summary

Adds interactive file type filtering to the TUI, addressing #486. Press T to open a type filter input in the footer where comma-separated file extensions can be entered (e.g. go,yaml,json). This mirrors the existing name filter (/ key) interaction pattern.

What changed

• tui/filter.go: Added showTypeFilterInput(), hideTypeFilterInput(), matchesTypeFilter(), and rebuildFooter(). Refactored existing name filter methods to use rebuildFooter() for clean coexistence of both inputs. Added "Name: " label prefix to the existing name filter input for clarity.
• tui/show.go: Added type filter check in showDir() rendering loop (directories always pass through, files filtered by extension). Added T to help text. Added active type filter display in footer. Extracted formatTypeFilterInfo() to keep showDir() within cyclomatic complexity limits.
• tui/keys.go: Added T keybinding in handleMainActions(). Updated handleFiltering() to support TAB cycling for both filter inputs. Updated the filtering guard to check both filter states.
• tui/tui.go: Added typeFilterValue, typeFiltering, typeFilteringInput fields. Updated fileItemSelected() to clear type filter on directory navigation.

Behavior

Action	Result
Press T	Opens "Type: " input in footer
Type go,yaml	Real-time filtering — only .go and .yaml files shown, all directories remain visible
ESC	Cancels and clears the type filter
Enter	Confirms filter, returns focus to table
TAB	Cycles focus back to a confirmed filter input
Navigate into a directory	Both name and type filters are cleared
Both / and T active	Both filters apply simultaneously (AND logic)

Extensions are case-insensitive, leading dots optional (both go and .go work), files without extensions are hidden when a type filter is active.

Tests

Added 7 new test functions in tui/filter_test.go:

• TestTypeFiltering — core filtering with single and multi-type values
• TestTypeFilteringWithoutCurrentDir — guard against nil currentDir
• TestTypeFilteringKeyBinding — T key activates the filter
• TestExitTypeFiltering — ESC clears filter state
• TestTypeFilterTabSwitch — TAB focus cycling
• TestBothFiltersCoexist — name + type filters applied simultaneously
• TestMatchesTypeFilter — unit tests for extension matching (case, dots, empty, dirs)

All existing tests pass. golangci-lint clean. Race detector clean.

Closes #486

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.66%. Comparing base (ede21d2) to head (818e9e0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
+ Coverage   81.42%   81.66%   +0.23%     
==========================================
  Files          49       49              
  Lines        5126     5197      +71     
==========================================
+ Hits         4174     4244      +70     
- Misses        816      817       +1     
  Partials      136      136              

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[ShivamB25]

Added follow-up tests to address the Codecov patch gap in tui/filter.go.

• covered showTypeFilterInput() no-color branch (!ui.UseColors)
• covered showTypeFilterInput() changed-callback path via input handler typing
• covered re-showing existing type filter input path

Local verification after this commit:

• golangci-lint run -c .golangci.yml ✅
• go test -v -race -covermode=atomic ./... ✅
• go test ./tui -coverprofile=/tmp/tui.cover reports 0 uncovered blocks in tui/filter.go ✅

Please let CI/Codecov refresh on latest head 818e9e0.

[dundee]

Nice PR, thank you!