fix(powernap): handle workspace/workspaceFolders and guard router on nil params

[csacca]

Summary

• powernap advertises workspaceFolders but didn’t handle the server-initiated workspace/workspaceFolders request. Some servers (e.g., MATLAB-language-server) call it early and hit ‘no handler’.
• Router.Route also dereferenced nil params, so requests/notifications without params could panic.

Changes

• lsp/client.go: register a handler for workspace/workspaceFolders that returns the configured folders or [].
• transport/router.go: make params nil-safe for both requests and notifications.

Tests

• Added coverage for handler registration and behavior, plus nil params in the router:
  • powernap/pkg/lsp/{client_setup_test.go,client_workspacefolders_test.go,client_workspacefolders_negative_test.go,client_workspacefolders_e2e_test.go,testutil_test.go}
  • powernap/pkg/transport/router_test.go

Verification

• GOTOOLCHAIN=go1.24.5 go test ./powernap/...
• Optional: run against a server that calls workspace/workspaceFolders with no params; no error/panic, folders returned.

Notes

• No breaking changes.
• Closes powernap advertises workspace/workspaceFolders but lacks handler; router panics on nil params #610.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.62%. Comparing base (4542a18) to head (46ca69d).
⚠️ Report is 279 commits behind head on main.

Files with missing lines	Patch %	Lines
powernap/pkg/lsp/client.go	50.00%	1 Missing and 2 partials ⚠️
powernap/pkg/transport/router.go	50.00%	2 Missing and 1 partial ⚠️

❗ There is a different number of reports uploaded between BASE (4542a18) and HEAD (46ca69d). Click for more details.

HEAD has 70 uploads less than BASE

Flag	BASE (4542a18)	HEAD (46ca69d)
	73	3

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #611       +/-   ##
==========================================
- Coverage   31.33%   0.62%   -30.71%     
==========================================
  Files         160      14      -146     
  Lines       14433    4137    -10296     
==========================================
- Hits         4523      26     -4497     
+ Misses       9628    4108     -5520     
+ Partials      282       3      -279     

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