Add P0 workplan bugs/tasks for MCP wrapper debug issues

[Copilot]

Documents three P0 bugs discovered during MCP debugging and creates corresponding implementation tasks in SPECS/Workplan.md.

Bug Tracker Entries

• BUG-T5: Empty-content tool results (result.content: []) skip structuredContent injection, violating strict MCP client expectations
• BUG-T6: Web UI port collisions from orphaned wrapper processes create noisy bind failures that destabilize MCP startup
• BUG-T7: Unsupported resources/* methods return tool-style result.isError payloads instead of standard JSON-RPC error envelopes

Implementation Tasks

• FU-P13-T7: Fix transformation logic to inject structuredContent fallback for empty-content tool results
• FU-P13-T8: Add deterministic collision handling for occupied Web UI ports (explicit error or safe fallback)
• FU-P13-T9: Normalize unsupported non-tool method failures into canonical JSON-RPC error responses

All tasks are P0 priority and selectable via scripts/pick_next_task.py --list.

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