fix(#2873): close review findings across fences, sanitizer and docs

Isolated security review found resolveSpecRootReference's fence tracker
toggled on any delimiter, so a backtick fence could be closed by a tilde
one and an include in the gap was rewritten inside a code block. Fixed by
reusing scanFencedBlocks - the canonical engine already behind
stripFencedCode and extractFencedBlock - rather than carrying a fourth
copy of fence detection, which also closes the duplication the standards
review flagged.

sanitizeForRender now strips combining marks and zero-width characters
alongside the ANSI, control and bidi classes it already handled.

Adds the C, E and F matrix rows the spec review found missing, including
installer-level coverage that spawns the real install rather than calling
the report builder. Ships the how-to, the reference and command docs in
five locales, the changeset, the inventory and glossary entries, and
regenerates health.md for the new W028 rule.

Refs #2873

docs/README.md

@@ -37,6 +37,7 @@ Language versions: [English](README.md) · [Português (pt-BR)](pt-BR/README.md)
 - [Isolate work with workspaces](how-to/isolate-work-with-workspaces.md) — use workspaces to sandbox experimental or risky changes
 - [Debug a failed execution](how-to/debug-a-failed-execution.md) — diagnose and recover from broken or incomplete phase execution
 - [Interpret scope-conformance warnings](how-to/interpret-scope-conformance-warnings.md) — read the advisory the worktree-wave merge emits when a plan branch commits outside its declared scope
+- [Interpret install-shadow warnings](how-to/interpret-install-shadow-warnings.md) — read the advisory GSD Core emits when a `/gsd-*` trigger is installed at both scopes and one silently wins, and tell "nothing to report" apart from "could not look"
 - [Interpret `state validate` results](how-to/interpret-state-validate-results.md) — read the `scope` reason codes and tell "nothing to report" apart from "could not look"
 - [Spike and sketch](how-to/spike-and-sketch.md) — use `/gsd-spike` and `/gsd-sketch` for exploratory work before committing to a plan
 - [Design a UI phase](how-to/design-a-ui-phase.md) — use the UI phase loop for frontend and visual work