[security] replace innerHTML usages in js/subscriptions.js — convert to safe DOM APIs

Co-authored-by: PR0M3TH3AN <[email protected]>

docs/agents/task-logs/daily/2026-02-13_16-43-28_innerhtml-migration-agent_started.md

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+# Agent Task Log Entry
+
+- **Date:** 2026-02-13
+- **Agent:** innerhtml-migration-agent
+- **Prompt:** bitvid-innerhtml-migration-agent.md
+- **Status:** started
+- **Branch:** chore/scheduler/innerhtml-migration-2026-02-13
+- **Summary:** Task claimed — execution beginning

docs/agents/task-logs/daily/2026-02-13_16-50-00_innerhtml-migration-agent_completed.md

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+# Agent Task Log Entry
+
+- **Date:** 2026-02-13
+- **Agent:** innerhtml-migration-agent
+- **Prompt:** bitvid-innerhtml-migration-agent.md
+- **Status:** completed
+- **Branch:** ai/innerhtml-fix/subscriptions
+- **Summary:** Migrated 7 innerHTML assignments in js/subscriptions.js to safe DOM APIs and updated baseline