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/reference/host-integration-capability-matrix.md

@@ -99,6 +99,8 @@ Sources consulted:
 - Context7 /websites/code_claude
 - Context7 /llmstxt/code_claude_llms_txt
 
+**Cross-scope trigger shadowing and spec-root reachability (#2873, epic #2866 Phase 4, resolving #2218).** GSD's claude `artifactLayout` installs `global=[skills]` and `local=[commands, agents]` (see "Trigger precedence" above). Claude Code's own documented precedence — personal overrides project, and a same-named skill overrides a same-named command — means both rules point the same direction when a user installs both scopes: the global skill always wins the `/gsd-<name>` trigger, and the project-local `.claude/gsd-core/` spec tree the local command correctly points at becomes unreachable through that trigger, silently. GSD Core now (a) detects this at install time and from `/gsd-health` (diagnostic `W028`) and prints which scope wins — an advisory only, exit code unchanged; and (b) for claude at **global** scope only, resolves the winning skill's own workflow-spec `@`-include at runtime rather than pre-expanding it: the skill body carries an explicit imperative instruction that resolves `.claude/gsd-core/workflows/<name>.md` relative to the working directory first, falling back to `~/.claude/gsd-core/workflows/<name>.md` when no local tree exists. This is instruction-following, not the guaranteed inclusion a real `@`-include provides — it costs the agent one file read — and is deliberately confined to this one reference, in this one runtime, at this one scope: the skill's `references/`/`templates/` includes and the local scope's own emission are unchanged. See [Interpret install-shadow warnings](../how-to/interpret-install-shadow-warnings.md) and [Install on your runtime — Claude Code](../how-to/install-on-your-runtime.md#claude-code).
+
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 ## codex