Add Looker WASM plugin

[daltoniam]

Summary

Initial Looker BI plugin for the daltoniam Switchboard marketplace — 23 tools across search, folders, Looks, dashboards, queries, SQL Runner, LookML models, connections, users, and scheduled plans.

• Auth uses Looker's API3 client_id/client_secret login flow with a process-scoped token cache that auto-refreshes on 401.
• All _run_* and _create_* tools clamp limit to a max of 5,000 rows (default 100) to prevent runaway responses.
• Includes compaction specs for every read endpoint (none on result-returning tools so analytics rows pass through untouched).
• Prebuilt dist/looker.wasm (~217 KB), manifest entry, and per-plugin README included.

Tools

Domain	Tools
Search	looker_search_content (entry point)
Folders	looker_list_folders, looker_get_folder
Looks	looker_list_looks, looker_get_look, looker_run_look
Dashboards	looker_list_dashboards, looker_get_dashboard
Queries	looker_run_inline_query (BI entry point), looker_run_query, looker_get_query, looker_create_query
SQL Runner	looker_run_sql_query
Models	looker_list_models, looker_get_model, looker_get_model_explore
Connections	looker_list_connections, looker_get_connection
Users	looker_get_me, looker_list_users, looker_get_user
Schedules	looker_list_scheduled_plans, looker_get_scheduled_plan

Test plan

• cargo build --release --target wasm32-wasip1 -p looker-wasm succeeds
• cargo clippy --target wasm32-wasip1 --all -- -D warnings clean
• cargo fmt --check clean
• Smoke test against Switchboard host runtime (wasm.Runtime.LoadModule):
  • name() returns "looker"
  • metadata() returns abi_version: 1, all credential keys, plaintext keys, placeholders
  • tools() returns 23 definitions
  • configure() rejects missing base_url and accepts a valid one (auto-appends /api/4.0)
  • execute() returns a structured error for unknown tools and missing required args
• Live test against a real Looker instance (will validate after merge)