Remove MCP transport and related dead code from experimental/aitools (#4688)

## Summary

- Remove MCP protocol SDK, server, providers, trajectory tracking, and
middleware
- Remove `init_template` subcommand and appkit templates
- Remove orphaned helper functions, unused prompt templates, and stale
docs
- Make `aitools install` an alias for `aitools skills install`

## What's deleted

- `lib/mcp/` — MCP protocol SDK (server, transport, protocol, types,
middleware)
- `lib/server/` — MCP server wrapper (lifecycle, health)
- `lib/providers/` — provider registry + clitools provider
- `lib/trajectory/` — local telemetry (tool call history)
- `lib/errors/` — JSON-RPC error types
- `lib/middlewares/middleware.go` — MCP-only middlewares
- `lib/config.go` — empty Config struct for MCP server
- `cmd/init_template/` — template initialization command
- `templates/` — appkit template (~15k lines)
- `docs/` — MCP-centric documentation
- 7 unused prompt templates
- Orphaned helper functions in `databricks_client.go`, `common/`,
`prompts/`, `session/`
- `acceptance/apps/init-template/` tests

## What stays

- CLI commands: `tools` (`query`, `discover-schema`,
`get-default-warehouse`), `skills`, `install`
- Libraries: `agents/`, `installer/`, `detector/`, `prompts/` (core),
`session/`, `middlewares/warehouse.go`,
`middlewares/databricks_client.go`, `pathutil/`
- Docs: `README.md` remains, but is rewritten for the reduced `aitools`
surface

## Upgrade note

- `databricks experimental aitools install` now installs Databricks
skills rather than the removed MCP server.
- If you previously installed the MCP server, remove stale
`databricks-mcp` config. For Claude Code: `claude mcp remove --scope
user databricks-mcp`. For Cursor: remove the `databricks-mcp` entry from
`~/.cursor/mcp.json`.

## Test plan

- [x] `go build ./experimental/aitools/...`
- [x] `make test-exp-aitools` (123 tests pass)
- [x] `make lintfull` (0 issues)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: arsenyinfo

.wsignore

@@ -11,7 +11,6 @@ python/docs/images/databricks-logo.svg
 # Binary files
 **/*.zip
 **/*.whl
-**/*.png
 
 # new lines are recorded differently on windows and unix.
 # In unix: "raw_body": "hello, world\n"