feat(tools): rewrite wire-visible tool names to internal opencode names

Introduces src/tools/wire-names.ts as the single source of truth for the
tool-name bidirectional mapping and replaces the 'strip mcp_ prefix'
behavior in src/response/mcp.ts with a full alias-aware rewrite.

The previous mcp-prefix stripper only knew how to remove a single
hard-coded prefix; it could not convert Claude's PascalCase wire names
(Bash, Read, Grep, etc.) back to the lowercase internal form that the
rest of opencode expects. Tool-use content blocks in responses now
survive both directions of the rewrite.

Source
- src/tools/wire-names.ts (new): toWireToolName / toInternalToolName
  pair. NATIVE_WIRE_NAME_BY_INTERNAL covers the 7 native tools (bash,
  read, glob, grep, edit, write, skill). PRESERVED_WIRE_NAMES keeps
  advisor + tool_search_tool_regex intact on both sides.
  detectLegacyDoublePrefix throws TypeError for mcp_mcp_* inputs.
  Pascal-case fallback converters handle anything outside the explicit
  allowlist.
- src/response/mcp.ts: stripMcpPrefixFromToolNameField becomes
  rewriteWireToolNameField, routing through toInternalToolName.
  stripMcpPrefixFromToolUseBlock and
  stripMcpPrefixFromToolReferenceBlock now rewrite rather than strip.

Tests
- tests/unit/tools/wire-names.test.ts: covers the 7-tool mapping,
  Pascal-case round-trip, preserved wire names, legacy-prefix
  stripping, and double-prefix error.
- tests/unit/request/wire-tool-naming.test.ts: end-to-end coverage
  through transformRequestBody and stripMcpPrefixFromJsonBody.

7/7 tests pass.