fix(graph): skip malformed tunnel records

[fallenmi]

What does this PR do?

• validates each decoded tunnels.json entry centrally in _load_tunnels
• keeps legacy-compatible records with a non-empty string ID and complete string wing/room endpoints
• preserves all optional fields, including older records without kind, timestamps, drawer IDs, or dynamics
• skips unusable records with one aggregated warning containing only the file path and count
• warns on unsupported top-level JSON types without auto-wrapping or logging payload contents
• adds regressions proving create, filtered list, follow, and delete remain usable when valid and malformed records coexist

The root cause was that _load_tunnels validated only the outer list. Consumers then called .get or indexed endpoint keys on arbitrary JSON elements, so one null, string, phantom dict, or partial endpoint blocked every valid tunnel behind it and surfaced through MCP as an internal tool error.

Read-only list/follow calls do not rewrite the sidecar. A later create/delete persists the filtered valid set through the existing atomic write path, matching the loader's established fail-soft recovery behavior. Unsupported non-list roots remain unsupported; changing destructive recovery for those files is intentionally outside this patch.

Closes #2266

How to test

• .venv/bin/python -m pytest -q tests/test_palace_graph_tunnels.py — 59 passed
• .venv/bin/python -m pytest -q tests/test_closets.py tests/test_miner.py — 202 passed
• .venv/bin/python -m pytest -q tests/test_mcp_server.py — 368 passed
• broad regression run excluding the unrelated installation-layout subprocess check — 4,299 passed, 31 skipped
• .venv/bin/pre-commit run --all-files — Ruff check and format passed

Checklist

• Tests pass
• No hardcoded paths
• Linter passes