refactor(skills): portable script paths via ${CLAUDE_SKILL_DIR}

Replace literal `.claude/skills/<owner>/...` paths in SKILL.md with the
`${CLAUDE_SKILL_DIR}` variable that Claude Code substitutes at invocation
time. Same-skill references become `${CLAUDE_SKILL_DIR}/<rest>`,
cross-skill references (erf-* → epf-*) become
`${CLAUDE_SKILL_DIR}/../<other>/<rest>`. All paths now wrapped in double
quotes to handle install locations with spaces.

This unblocks plugin-mode installation: literal `.claude/skills/...`
paths fail when the skill is loaded from `~/.claude/plugins/cache/...`
or from a personal `~/.claude/skills/` install. Drop-in mode continues
to work because Claude Code resolves the variable in all install scopes.

Verified via pilot:
- Project drop-in (cc-1c-skills repo)
- Personal `~/.claude/skills/cf-info/`
- Plugin via `/plugin marketplace add <local-path>`

Scope: 61 SKILL.md, 125 path replacements (8 cross-skill).
Scripts unchanged — they already use \$PSScriptRoot and ../<sibling>
patterns that resolve correctly under the bundled cache layout.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/skills/web-test/SKILL.md

@@ -17,7 +17,7 @@ Automates user interactions with 1C:Enterprise web client via Playwright — nav
 ## Quick start
 
 ```bash
-RUN=".claude/skills/web-test/scripts/run.mjs"
+RUN="${CLAUDE_SKILL_DIR}/scripts/run.mjs"
 
 # One-shot: opens browser → runs script → closes browser → exits
 node $RUN run http://localhost:8081/bpdemo test-scenario.js
@@ -35,7 +35,7 @@ SCRIPT
 ## Setup (first time)
 
 ```bash
-cd .claude/skills/web-test/scripts && npm install
+cd "${CLAUDE_SKILL_DIR}/scripts" && npm install
 ```
 
 Requires Node.js 18+. `npm install` downloads Playwright and Chromium.