Wire --projectRoot into the remaining discover-site-components consumers

The site-referenced table discovery (this PR) made discover-site-components
return customTables (and thus missing.customTables) ONLY when --projectRoot (or
--datamodelManifest) is passed — without a local signal it returns [] rather than
the old publisher-prefix dump. setup-solution Step D was updated to pass
--projectRoot, but three other consumers that read missing.customTables were
missed, so their "custom tables missing from the solution" completeness check
silently reported 0 for every site:
- export-solution Phase 2.5 (pre-export completeness)
- plan-alm Phase 1 (pre-plan completeness)
- deploy-pipeline Phase 3.5 (pre-sync completeness)

Added --projectRoot "." to all three so the check is restored with the correct
site-scoped count. (setup-solution Phase 5.4b/5.4c calls consume missing.envVars /
missing.powerpagecomponents / siteLanguages, not customTables, so they're correct
as-is with --publisherPrefix/--solutionId.)

1211 tests pass, alm-lint 0 findings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: tyaginidhi

plugins/power-pages/skills/deploy-pipeline/SKILL.md

@@ -300,7 +300,8 @@ node "${CLAUDE_PLUGIN_ROOT}/scripts/lib/discover-site-components.js" \
   --envUrl "{devEnvUrl}" --token "{DEV_TOKEN}" \
   --siteId "{websiteRecordId from .solution-manifest.json}" \
   --publisherPrefix "{publisherPrefix from .solution-manifest.json}" \
-  --solutionId "{solutionId from .solution-manifest.json}"
+  --solutionId "{solutionId from .solution-manifest.json}" \
+  --projectRoot "."
 ```
 
 Parse stdout and evaluate `missing.*`. **Before doing anything else**, capture the **pre-sync state** so a post-sync re-confirmation gate can show what changed:

plugins/power-pages/skills/export-solution/SKILL.md

@@ -158,7 +158,8 @@ node "${CLAUDE_PLUGIN_ROOT}/scripts/lib/discover-site-components.js" \
   --envUrl "{envUrl}" --token "{token}" \
   --siteId "{websiteRecordId}" \
   --publisherPrefix "{publisherPrefix from .solution-manifest.json}" \
-  --solutionId "{solutionId}"
+  --solutionId "{solutionId}" \
+  --projectRoot "."
 ```
 
 Parse stdout and evaluate `missing`. **Before doing anything else**, capture the **pre-sync state** so a post-sync re-confirmation gate can show what changed:

plugins/power-pages/skills/plan-alm/SKILL.md

@@ -242,7 +242,8 @@ Steps:
       --envUrl "{envUrl}" --token "{token}" \
       --siteId "{websiteRecordId from powerpages.config.json}" \
       --publisherPrefix "{solutionManifest.publisher.prefix}" \
-      --solutionId "{solutionManifest.solution.solutionId}"
+      --solutionId "{solutionManifest.solution.solutionId}" \
+      --projectRoot "."
     ```
 
     Parse stdout and evaluate `missing.*`: