test: raise LSP package coverage past 80%

internal/lsp 65.5% to 94.4%: cursor context resolution, router dispatch
and error codes, document lifecycle handlers, workspace indexing, server
run loop and gopls diagnostics publishing, provider adapters.

internal/lsp/provider 57.0% to 88.2%: hover for every node kind,
definition and reference resolution with exact positions, semantic token
emission for Go code and AST nodes, search helper recursion.

internal/lsp/gopls 42.9% to 97.1%: proxy lifecycle and JSON-RPC round
trips against a fake gopls subprocess (the test binary symlinked as
gopls speaking framed JSON-RPC over stdio), request serialization,
virtual Go generation and position mapping.

internal/lsp/log 0% to 100%.

The remaining uncovered code is gopls-gated branches in lsp and provider
that require constructing the concrete GoplsProxy, plus fault-injection
error seams.