feat: add ROUTER_IGNORE_TOOL_IDS for tool-level filtering

[effortprogrammer]

Problem

grep_app MCP's searchGitHub tool searches all of GitHub instead of the local codebase. The BM25 router picks it up on keywords like "search", "code", "find" — returning results from unrelated repos (actix-web-demo, VictoriaMetrics, etc.).

Users could only block the entire server via ROUTER_IGNORE_IDS=grep_app, losing other useful tools from the same server.

Additionally, reenableOhMyOpencodeMcps() was force-re-enabling built-in MCPs that users had intentionally disabled.

Solution

1. New env var: ROUTER_IGNORE_TOOL_IDS

• Format: ROUTER_IGNORE_TOOL_IDS=serverId:toolName,serverId2:toolName2
• Example: ROUTER_IGNORE_TOOL_IDS=grep_app:searchGitHub
• Filters tools at registration time — they never enter the BM25 index
• Other tools from the same server remain available

2. Remove reenableOhMyOpencodeMcps postWriteHook

• Was overriding user config by force-re-enabling built-in MCPs
• User settings should always be respected

Files Changed

• router.py — Core filtering in sync_from_tool_definitions
• hub.py — Stores and passes ignore_tool_ids through the chain
• opencode_gateway_server.py — Parses env var
• router_mcp_server.py — Parses env var (standalone mode)
• index.ts — Removes reenableOhMyOpencodeMcps hook

[effortprogrammer]

Closing in favor of PR #15 (hybrid search) — rule-based blocklist doesn't scale. Will verify hybrid search properly handles tool disambiguation.