docs(#3309): disclose hardcoded-slash-command fidelity reduction consistently

root-existence.cts (E002, E003) and phase-structure.cts (W009) hardcode
a canonical hyphen-form slash command in their ADVISE remedy, same as
config-validation.cts's already-disclosed W016 — forced by §8.1 rule 1
(a Rule's check(snapshot) cannot call the runtime-resolved slash()
formatter, which needs cwd). Only config-validation.cts's own header
disclosed this tradeoff; the other two sites had it happen without
recording it in their own file. Adds the same disclosure to both,
matching the established convention. No behavior change.

src/health-diagnostic-rules/phase-structure.cts

@@ -31,6 +31,16 @@
  *   `verificationStatus`) — a disclosed fidelity reduction, not a silent
  *   reproduction of the original six-way label.
  *
+ * W009's original message interpolates `${slash('plan-phase')}`
+ * (`verify.cts:1982`, ``Re-run ${slash('plan-phase')} with --research to
+ * regenerate``), a per-project runtime-resolved value (`formatGsdSlash`,
+ * `src/runtime-slash.cts`) this rule's `(snapshot) => Diagnostic[]`
+ * signature has no access to. Hardcodes the canonical `/gsd-plan-phase`
+ * hyphen form instead, mirroring the sibling "config.json validation"
+ * group's W016 rule (`src/health-diagnostic-rules/config-validation.cts`),
+ * which hardcodes `/gsd-ai-integration-phase` the same way for the
+ * identical reason.
+ *
  * Design: .gsd/phase/refactor-3309-health-diagnostic-rule-table/40-design.md
  *
  * ADR-457 build-at-publish: source in

src/health-diagnostic-rules/root-existence.cts

@@ -10,6 +10,18 @@
  * Ported behavior-preserving from `cmdValidateHealth`
  * (`src/verify.cts:1681-1705`), the exact call sites for E002/E003/E004/W001.
  *
+ * E002's original message interpolates `${slash('new-project')}`
+ * (`verify.cts:1682`, ``Run ${slash('new-project')} to create``) and E003's
+ * interpolates `${slash('new-milestone')}` (`verify.cts:1694`, ``Run
+ * ${slash('new-milestone')} to create roadmap``) — both per-project
+ * runtime-resolved values (`formatGsdSlash`, `src/runtime-slash.cts`) this
+ * rule's `(snapshot) => Diagnostic[]` signature has no access to (§8.1 rule
+ * 1 forbids ambient I/O, including `cwd`, inside `check`). Hardcodes the
+ * canonical `/gsd-new-project`/`/gsd-new-milestone` hyphen form instead,
+ * mirroring the sibling "config.json validation" group's W016 rule
+ * (`src/health-diagnostic-rules/config-validation.cts`), which hardcodes
+ * `/gsd-ai-integration-phase` the same way for the identical reason.
+ *
  * Design: .gsd/phase/refactor-3309-health-diagnostic-rule-table/40-design.md
  *
  * ADR-457 build-at-publish: source in src/health-diagnostic-rules/root-existence.cts,