feat: complete native execution and Steam discovery

docs/phase-3/evidence-2026-07-18.md

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+# Phase 3 Steam discovery evidence
+
+- Date: 2026-07-18
+- Requirement IDs: R-005, R-009, R-012, R-016, R-024, R-027
+- Phase/gate: phase 3 / read-only Steam discovery
+- Scope: native Steam-root selection, bounded `libraryfolders.vdf` and
+  `appmanifest_*.acf` parsing, installed-title normalization, stable App ID and
+  installation identity, provider-scoped CLI discovery, and hostile fixtures
+- Exclusions: Steam process startup, launch plans, game execution, Proton selection,
+  lifecycle tracking, account data, artwork, and Steam configuration mutation
+- Commands: `cargo test --workspace --all-targets --locked`; `kiln scan --provider
+  steam --json`; `make check`
+- Expected result: missing/unmounted libraries are skipped; partial installs and known
+  Steam runtime packages are excluded; malformed, duplicate, oversized, invalid-UTF-8,
+  traversal, and symlinked metadata fail closed; installed games normalize without
+  starting Steam
+- Observed result: 61 automated tests passed; the production CLI parsed the current
+  local Steam metadata and reported 227 installed titles without starting Steam or a
+  game; a real trailing-space display-name case was normalized and retained as a fixture
+- Result: pass