feat: add workspace_symbol, implementation, and call_hierarchy tools

[scgm11]

What

Surfaces three LSP methods this bridge already wraps at the client layer but doesn't expose as MCP tools.

• workspace_symbol(query) — fuzzy symbol search across the workspace via workspace/symbol. Use BEFORE definition / references when you don't know which file a symbol lives in: one call replaces a grep -r "func MyFunc\|type MyFunc\|var MyFunc" scan. gopls / tsserver / clangd all support fuzzy matching by default.
• implementation(filePath, line, column) — find every type or method that satisfies the interface at the given position via textDocument/implementation. Critical for Go and TypeScript: structural typing has no implements keyword for grep to match, so this is the only AST-aware path to enumerate an interface's satisfaction set.
• call_hierarchy(filePath, line, column) — list direct callers AND callees of a function via the 3-call LSP dance (prepareCallHierarchy → incomingCalls + outgoingCalls). Output mirrors gopls call_hierarchy: caller[N]: …, identifier: …, callee[N]: … markers.

Why

These three are the most-asked questions an editor's "Go to symbol", "Go to implementation", and "Show call hierarchy" buttons answer — and the LSP methods to power them are already in internal/lsp/methods.go (Symbol, Implementation, PrepareCallHierarchy, IncomingCalls, OutgoingCalls). Wrapping them as MCP tools means an agent driving this bridge gets the same surface a human gets in vscode/zed.

I'd been maintaining an out-of-tree fork to add these for our project's Claude Code wiring; opening this PR so it can live upstream instead.

How

• Three new internal/tools/*.go files — thin wrappers around the existing client methods, following the exact shape of hover.go (URI scheme, 1→0 indexed conversion, client.OpenFile before position-based calls, error formatting).
• Three new mcp.NewTool(...) registrations in tools.go, mirroring the hover / rename_symbol registration pattern (string + numeric args with float64/int type switching).
• Small interface change in internal/protocol/interfaces.go: WorkspaceSymbolResult gains GetKind() and GetContainerName() methods. Both concrete types (WorkspaceSymbol and SymbolInformation) already have the underlying fields, so the implementation is two lines each. The new methods let workspace_symbol render results as <file>:<line>:<column> <name> <Kind>[ (in <ContainerName>)] — the canonical editor-symbol-picker format.

Verified

• go build ./... clean.
• go vet ./... clean.
• go test ./internal/... — every existing test still green.
• Built binary + MCP handshake against gopls (workspace = a 7923-file Go monorepo): tools/list returns 9 tools (the original 6 + the 3 new ones), each with the documented input schema. Sample workspace_symbol "ExpectedSchemaVersion" returns 4 matches (the constant + 3 tests).
• Output formats match the gopls CLI's workspace_symbol / implementation / call_hierarchy subcommand output, so callers that already parse gopls CLI output don't need to rewrite their parser.

Compatibility

• Interface change to WorkspaceSymbolResult is internal — only WorkspaceSymbol and SymbolInformation implement it, both controlled by this repo. No breaking changes to public consumers.
• All new tools follow the documented MCP schema patterns (mcp.WithDescription / mcp.WithString / mcp.WithNumber / mcp.Required).
• LocationLink fallback path in implementation.go handles servers that advertise linkSupport=true (rust-analyzer, clangd).

🤖 Generated with Claude Code