feat(cli): expose slash search in provider and model pickers

[kfallah]

Summary:

• Advertise the / search shortcut in the shared provider/model picker UI.
• Support /query and a standalone / prompt in the line-based fallback.
• Cover single-select and multi-select search behavior.

Verification:

• uv run --extra dev ruff check .
• uv run --extra dev ty check
• 121 picker/provider/model tests and 9 picker-view tests pass outside the pre-existing Rich PTY cleanup assertions.

[greptile-apps]

Greptile Summary

The PR exposes slash-search guidance in provider and model pickers and adds explicit slash-prefixed searching to the line-based fallback.

• Handles /query before numeric row parsing in single- and multi-select pickers.
• Supports a standalone / that opens a dedicated search prompt.
• Adds focused coverage for slash searching and picker hints.

Confidence Score: 5/5

The PR appears safe to merge.

The previously reported numeric slash-search defect is fixed because slash-prefixed input is now handled and continued before numeric position parsing in both picker modes, and no blocking failure remains.

Important Files Changed

Filename	Overview
exp/cli/shared/picker.py	Adds slash-prefixed and standalone-slash search handling before numeric position parsing in both line-based picker modes.
exp/cli/shared/picker_test.py	Covers slash-prefixed, standalone-slash, and numeric slash searches for single- and multi-select pickers.
exp/cli/shared/picker_view.py	Advertises the slash-search shortcut in keyboard picker hints.
exp/cli/shared/picker_view_test.py	Verifies that both keyboard picker variants display the slash-search hint.
exp/cli/providers/provider_picker_test.py	Verifies that the provider picker exposes the shared slash-search guidance.

_{Reviews (2): Last reviewed commit: "fix(cli): keep numeric slash queries in ..." | Re-trigger Greptile}