feat: add partial context matching to switch command

[davidblum]

Overview

Adds partial context matching to the switch command. When a context argument is provided, it first tries an exact match (switches immediately without the picker). If no exact match, it filters contexts by case-insensitive substring and opens the fuzzy picker with only the matches.

Based on the store-env-vars branch (#1), so includes KUBESWITCH_STORE and KUBESWITCH_PATH support.

Originally submitted upstream as danielfoehrKn#194, rebased onto the store-env-vars work.

Technical

• Adds desiredContext parameter to Switcher() function
• Routes args through Switcher() instead of setContextCmd for unified handling
• Exact match: bypasses fuzzy picker entirely
• Partial match: filters the global context list, then opens the picker with reduced set
• waitForSearchResults() helper ensures async search has populated before matching
• All return paths include store name and source path (from feat: expose store name and source path as env vars #1)

Testing

• go build ./... passes
• go test ./... passes
• switch aws-otk-prod-dx-use1-004 switches immediately (exact match)
• switch prod-dx opens picker filtered to matching contexts (partial match)
• switch nonexistent returns error "no contexts matching"
• switch with no args opens normal fuzzy picker (unchanged behavior)
• KUBESWITCH_STORE and KUBESWITCH_PATH set correctly for all paths