feat(lsp): LSP capability seam, generic stdio provider, and lsp tool

Implements the LSP capability seam RFC as three packages: dsh-lsp (the
ctx.lsp interface — provider registry by branded id + exclusive extension
mapping, per-query order-independent selection, closed request/result
vocabulary, LspError taxonomy), dsh-lsp-local (a generic stdio language-server
provider — Content-Length JSON-RPC framing, per-(provider, workspace) process
single-flight, transient didOpen/query/didClose, an abortable per-instance
queue, UTF-16 negotiation, host-namespace source reads outside ctx.fs, and
bounded shutdown/kill teardown), and dsh-tool-lsp (the model-facing lsp tool —
four operations, one-based UTF-16 cursor conversion, workspace-grouped location
rendering, hover capping, a required session workspace, and a timeout budget).

Why: an agent had text search and file reads but no way to identify a program
symbol — follow an alias, connect an interface to implementations, or read an
inferred type — before changing code. Splitting model contract, seam, and local
subprocess behavior keeps the four semantic queries stable across future remote
or sandbox-native providers without leaking a JSON-RPC escape hatch.

tsconfig.json

@@ -94,6 +94,9 @@
     { "path": "./packages/hooks/hook-protocol" },
     { "path": "./packages/hooks/hooks-claude" },
     { "path": "./packages/hooks/hooks-codex" },
-    { "path": "./packages/mcp/mcp-client" }
+    { "path": "./packages/mcp/mcp-client" },
+    { "path": "./packages/lsp/lsp" },
+    { "path": "./packages/lsp/lsp-local" },
+    { "path": "./packages/lsp/tool-lsp" }
   ]
 }