Accept OpenCode model IDs in the T3 sheet

[ash663]

The T3 sheet checker rejects every OpenCode target. OpenCode names its models <provider>/<model>, so an entry for an OpenCode provider instance reads like opencode/openrouter/x-ai/grok-4.7. parseEntry allows only one /, so setup-pstack cannot write that line. A machine whose only Grok comes through OpenCode then cannot seat a third family on the panels.

What changed

• parseEntry splits an entry at its first / and keeps the rest as the model ID. A provider instance ID cannot contain /, so the split has one reading.
• family reads the last / part of the model ID. Without that, an OpenCode route prefix becomes part of the family: the model openrouter/anthropic/claude-opus-5-5 would count as a different family from claude-opus-5-5.
• The sheet section of t3-tools.md states both rules.

Tests

• tests/t3-sheet.test.mjs gains two cases. One checks that a slashed model ID parses and a trailing / is still rejected. The other checks that family ignores a route prefix. Both fail on main and pass on this branch.
• bun tools/generate.mjs --check: 90 generated files current.
• bun test tests/: 1217 pass, 54 skip, 0 fail.
• Not run: tests/skill-collision-repro.sh and tests/copilot-smoke.sh.

Versioning

VERSION and CHANGES.md are unchanged, so the fix ships with the next release and does not collide with #12.

[chhoumann]

Thank you @ash663! This landed unchanged through #15 and shipped in 1.0.14, together with the Pi test from #14. Credited in CHANGES.