Reduce syscalls in gomi -b restore path

[babarot]

WHAT

Eliminate redundant filesystem syscalls in the gomi -b restore flow by using cached file metadata, removing duplicate existence checks, and parallelizing storage listing.

WHY

Profiling showed gomi -b spent 85% of CPU time in syscalls (system 0.47s of 0.55s total CPU). Three sources of waste were identified:

1. rejectBySize called fs.DirSize() for every file — recursively walking directories to compute sizes, even though File.Size was already populated during List() via os.Stat(). The default config sets Max: "10GB", so this ran on every invocation.

2. Title() and Description() called os.Stat() on every render — BubbleTea re-renders visible items on each frame, causing V×2 stat calls per frame. File.IsDir from the initial List was sufficient.

3. loadFileListCmd re-checked file existence — os.Stat() on every file, duplicating the check already done by cli.filterFiles().

4. Storage backends listed sequentially — XDG and Legacy List() calls ran one after another instead of concurrently.

This PR also includes prior refactoring commits (design improvements from Phases 1-3).

[github-actions]

Code Metrics Report

	main (a73fb08)	#123 (97d3922)	+/-
Coverage	42.2%	42.6%	+0.3%
Code to Test Ratio	1:1.5	1:1.5	-0.1
Test Execution Time	3s	3s	0s

Details

  |                     | main (a73fb08) | #123 (97d3922) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          42.2% |          42.6% | +0.3% |
  |   Files             |             24 |             24 |     0 |
  |   Lines             |           1835 |           1840 |    +5 |
+ |   Covered           |            776 |            784 |    +8 |
- | Code to Test Ratio  |          1:1.5 |          1:1.5 |  -0.1 |
  |   Code              |           2720 |           2739 |   +19 |
- |   Test              |           4238 |           4216 |   -22 |
  | Test Execution Time |             3s |             3s |    0s |

Code coverage of files in pull request scope (38.3% → 38.9%)

Files	Coverage	+/-	Status
internal/trash/filter.go	50.3%	+2.9%	modified
internal/trash/legacy/history/history.go	42.5%	-0.3%	modified
internal/trash/legacy/storage.go	32.0%	+0.1%	affected
internal/trash/manager.go	41.7%	+2.4%	modified
internal/trash/storage.go	38.0%	-0.7%	modified
internal/trash/xdg/storage.go	32.3%	-0.6%	affected

---

Reported by octocov