feat(open): create open variant SKILL.md and reference files

Router SKILL.md dispatches to mode-specific references:
- research.md: one-shot research with --store for persistence
- watchlist.md: add/remove/list/run topics
- briefing.md: daily/weekly briefing generation
- history.md: query/search accumulated findings
- context.md: agent memory template

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

variants/open/context.md

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+# last30days Context
+
+Agent memory for improving research quality over time.
+
+## User Preferences
+<!-- Record preferences discovered during interactions -->
+<!-- e.g., "Prefers detailed technical analysis over general summaries" -->
+
+## Source Quality Notes
+<!-- Record which sources work best for which topics -->
+<!-- e.g., "r/LocalLLaMA is highest signal for AI hardware topics" -->
+<!-- e.g., "@kaboratech provides reliable AI tool reviews" -->
+
+## Interaction History
+<!-- Record topics researched and useful follow-up patterns -->
+<!-- e.g., "2026-02-14: Researched 'AI video tools', user wanted Runway vs Kling comparison" -->