test(e2e): assert the generate matrix covers every declared tool target

[saitota]

Background

Which tools a feature supports, and where each writes output, lives in two places — the implementation (getToolTargets()) and the hardcoded it.each arrays in src/e2e/*.spec.ts — with nothing connecting them. CLAUDE.md having to tell a human "preserve the Tool × Feature matrix tests" is the evidence it was never mechanized. So adding a tool (32 in H1 2026) means reconstructing from memory which specs need new rows; a miss leaves CI green while coverage silently drifts.

Changes

• Add assertGenerateMatrixCoversTargets (e2e-helper): derives the tool set from getToolTargets() and asserts declared targets partition exactly into the matrix's tested tools plus an explicit, reasoned untested list — a declared-but-absent tool or a stray entry now fails CI.
• Wire it into all 8 features (project + global where supported). -legacy aliases are excluded, as the supported-tools tables already do.

Same "derive from implementation, fail on drift" idiom as the TOOL_DISPLAY check and gitignore derivation. Per-tool expected paths stay hand-written; only the enumeration is derived.

Test Plan

• pnpm cicheck green (6740 tests).
• Verified drift detection: removing a tool from a matrix array fails with "declared by the processor but missing from the e2e matrix".

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[saitota]

Trimmed comments: now +1,318 / -884.